Zirconia layered body

ABSTRACT

There is provided at least any of a layered body which has a change in color tone and in which it is unnecessary to select a colorant and the content of the colorant in consideration of a difference in the sintering behavior between layers, a precursor thereof, or a method for producing these. Provided is a layered body which has a structure, in which two or more layers containing stabilizer-containing zirconia and a colorant are layered, and in which types and contents of the colorants contained in the layers are equal to each other, the layered body including at least: a first layer containing a colorant and zirconia which has a stabilizer content of higher than or equal to 3.3 mol %; and a second layer containing a colorant and zirconia which has a stabilizer content different from that of the zirconia contained in the first layer.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a composition in which layers ofzirconia are layered and to a zirconia layered body.

Description of Related Art

A zirconia (ZrO₂) sintered body is produced by molding raw materialpowder which mainly contains zirconia and sintering the molded rawmaterial powder. The raw material powder thermally shrinks and isdensified through heat treatment such as sintering or calcination. Thebehavior of the raw material powder during heat treatment differsdepending on the characteristics of the raw material powder,particularly the composition of the raw material powder.

Even with raw material powder in which there is only a difference in thecontent of additives of less than 0.1 wt %, in a case where a sinteredbody in which these raw material powder are layered is heat-treated,sintering behaviors among the layers are different from each other dueto the composition difference. In order to obtain a layered body havinga change in color tone without causing such failures, special adjustmentor treatment is required (for example, Patent Documents 1 and 2).

Patent Document 1 discloses that compositions and thermal shrinkagebehaviors of raw material powder are adjusted by coating the rawmaterial powder with a dopant, and the raw material powder are molded toobtain a sintered body consisting of a layered body having differentcolor tones. In addition, Patent Document 2 discloses that a sinteredbody, which consists of a layered body having a change in color tone andlayers having different contents of colorants, is obtained by layeringand molding layers by applying vibration so as to form a boundary layerin which powder of upper and lower layers are mixed with each other.

PATENT DOCUMENTS

[Patent Document 1] Published Japanese Translation No. 2016-527017 ofthe PCT International Publication

[Patent Document 2] Japanese Unexamined Patent Application, FirstPublication No. 2014-218389

SUMMARY OF THE INVENTION

The change in color tones is imparted to the layered bodies disclosed inPatent Documents 1 and 2 by changing the content of additives betweenlayers. However, in these layered bodies, it is necessary to select acolorant for each layer and the contents thereof in consideration ofdifferences in the sintering behavior between layers which are derivedfrom differences in the contents of the colorants in addition to adesired color tone.

An object of the present disclosure is to provide at least any of alayered body which has a change in color tone and in which it isunnecessary to select a colorant and the content of the colorant inconsideration of the difference in the sintering behavior betweenlayers, a precursor thereof, or a method for producing these. Fromanother viewpoint, another object of the present disclosure is toprovide at least any of a layered body which is suitable as a dentalprosthetic member, a precursor thereof, or a method for producing these.

The present inventors have focused on a state of zirconia, whichoccupies the majority of a layered body, when producing a layered bodyhaving a change in color tone. As a result, it is found that a change incolor tone is imparted to the layered body due to a mechanism differentthan that of a layered body in the related art, by layering raw materialpowder having different contents of stabilizers of zirconia.

That is, the gist of the present disclosure is as follows.

[1] A layered body which has a structure, in which two or more layerscontaining stabilizer-containing zirconia and a colorant are layered,and in which types and contents of the colorants contained in the layersare equal to each other, the layered body including at least: a firstlayer containing a colorant and zirconia which has a stabilizer contentof higher than or equal to 3.3 mol %; and a second layer containing acolorant and zirconia which has a stabilizer content different from thatof the zirconia contained in the first layer.

[2] The layered body according to [1], in which the content of thestabilizer of the stabilizer-containing zirconia contained in the secondlayer is 1.5 mol % to 7.0 mol %.

[3] The layered body according to [1] or [2], in which the content ofthe stabilizer of the stabilizer-containing zirconia contained in thesecond layer is 4.5 mol % to 7.0 mol %.

[4] The layered body according to any one of [1] to [3], in which thecontent of the stabilizer of the stabilizer-containing zirconiacontained in the first layer is 3.3 mol % to 5.5 mol %.

[5] The layered body according to any one of [1] to [4], in which adifference between the stabilizer content in the first layer and thestabilizer content in the second layer is greater than or equal to 0.2mol %.

[6] The layered body according to any one of [1] to [5], in which thestabilizer is one or more selected from the group consisting of yttria(Y₂O₃), calcia (CaO), magnesia (MgO), ceria (CeO₂), praseodymium oxide(Pr₆O₁₁), neodymium oxide (Nd₂O₃), terbium oxide (Tb₄O₇), erbium oxide(Er₂O₃), and ytterbium oxide (Yb₂O₃).

[7] The layered body according to any one of [1] to [6], in which thecolorant is at least any of a transition metal element or alanthanoid-based rare earth element.

[8] The layered body according to any one of [1] to [7], in which thecontent of the colorant is 0.01 wt % to 1.0 wt %.

[9] The layered body according to any one of [1] to [8], in which atleast one of the layers contains alumina.

[10] The layered body according to any one of [1] to [9], in which awarp measured using a thickness gauge according to JIS B 7524:2008 isless than or equal to 1.0 mm.

[11] The layered body according to any one of [1] to [10], in which awarp measured using a thickness gauge according to JIS B 7524:2008 isless than or equal to 0.2 mm.

[12] The layered body according to any one of [1] to [11], in which thelayered body is a sintered body.

[13] The layered body according to any one of [1] to [12], furtherincluding: a zirconia layer of which a total light transmittance withrespect to a CIE standard light source D65 at a sample thickness of 1.0mm is 30% to 50%.

[14] The layered body according to any one of [1] to [13], in which thelayered body is a calcined body.

[15] A method for producing the layered body according to any one of [1]to [13], including: a step of sintering a green body at 1,200° C. to1,600° C.,

wherein the green body has a structure, in which two or more powdercomposition layers consisting of a powder composition containing astabilizer-containing zirconia, a colorant, and a binding agent arelayered, and in which types and contents of the colorants contained inthe powder composition layers are equal to each other,

includes at least a first powder composition layer containing a bindingagent, a colorant, and zirconia which has a stabilizer content of higherthan or equal to 3.3 mol % and a second powder composition layercontaining a binding agent, a colorant, and zirconia which has astabilizer content different from that of the zirconia contained in thefirst powder composition layer, and

has a difference in a binding agent content between the first powdercomposition layer and the second powder composition layer exceeds 0.01wt %.

[16] A method for producing the layered body according to any one of [1]to [13], including: a step of calcining a green body at a temperature ofhigher than or equal to 800° C. and lower than 1,200° C. to obtain acalcined body;

and a step of sintering the calcined body at 1,200° C. to 1,600° C.,

wherein the green body has a structure, in which two or more powdercomposition layers consisting of a powder composition containing astabilizer-containing zirconia, a colorant, and a binding agent arelayered, and in which types and contents of the colorants contained inthe powder composition layers are equal to each other,

includes at least a first powder composition layer containing a bindingagent, a colorant, and zirconia which has a stabilizer content of higherthan or equal to 3.3 mol % and a second powder composition layercontaining a binding agent, a colorant, and zirconia which has astabilizer content different from that of the zirconia contained in thefirst powder composition layer, and

has a difference in a binding agent content between the first powdercomposition layer and the second powder composition layer exceeds 0.01wt %.

[17] A method for producing the layered body according to any one of [1]to [11] and [14], including: a step of calcining a green body at atemperature of higher than or equal to 800° C. and lower than 1,200° C.,

wherein the green body which has a structure, in which two or morepowder composition layers consisting of a powder composition containinga stabilizer-containing zirconia, a colorant, and a binding agent arelayered, and in which types and contents of the colorants contained inthe powder composition layers are equal to each other,

includes at least a first powder composition layer containing a bindingagent, a colorant, and zirconia which has a stabilizer content of higherthan or equal to 3.3 mol % and a second powder composition layercontaining a binding agent, a colorant, and zirconia which has astabilizer content different from that of the zirconia contained in thefirst powder composition layer, and

has a difference in a binding agent content between the first powdercomposition layer and the second powder composition layer exceeds 0.01wt %.

[18] The production method according to any one of [15] to [17], inwhich the binding agent is one or more selected from the groupconsisting of polyvinyl alcohol, polyvinyl butyrate, wax, and acrylicresin.

[19] The production method according to any one of [15] to [18], inwhich the powder composition contained in the powder composition layersis granulated powder.

[20] A dental material containing the layered body according to any oneof [1] to [12].

According to the present disclosure, it is possible to provide any of alayered body which has a change in color tone and in which it isunnecessary to select a colorant and the content of the colorant inconsideration of the difference in the sintering behavior betweenlayers, a precursor thereof, or a method for producing these.Furthermore, it is possible to provide at least any of a layered bodywhich is suitable as a dental prosthetic member, a precursor thereof, ora method for producing these.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a cross section of a sintered bodyhaving a structure in which two zirconia layers are layered.

FIG. 2 is a schematic diagram showing a cross section of a sintered bodyhaving a structure in which three zirconia layers are layered.

FIG. 3 is a schematic diagram showing a method for measuring a warp.

FIG. 4 is a schematic diagram showing a method for measuring athree-point bending strength.

FIG. 5 is a schematic diagram showing zirconia having a neckingstructure.

DETAILED DESCRIPTION OF THE INVENTION

A layered body of the present embodiment may be one or more selectedfrom the group consisting of a sintered body, a calcined body, and agreen body, and is preferably at least any of a sintered body or acalcined body. Here, in the present embodiment, a “layer containingstabilizer-containing zirconia and a colorant” may be regarded as a“zirconia layer containing stabilizer-containing zirconia and acolorant” in a case where the layered body is a sintered body, a“zirconia composition layer containing a colorant and zirconia whichcontains a stabilizer and has a necking structure” in a case where thelayered body is a calcined body, and a “powder composition layerconsisting of a powder composition containing stabilizer-containingzirconia, a colorant, and a binding agent” in a case where the layeredbody is a green body.

Hereinafter, the layered body of the present disclosure will bedescribed with reference to an example of an embodiment in which thelayered body is a sintered body.

In the present embodiment, the layered body is a sintered body which hasa structure, in which two or more zirconia layers containingstabilizer-containing zirconia and a colorant are layered, and in whichtypes and contents of the colorants contained in the zirconia layers areequal to each other, and includes at least: a first zirconia layercontaining a colorant and zirconia which has a stabilizer content ofhigher than or equal to 3.3 mol %; and a second zirconia layercontaining a colorant and zirconia having a stabilizer content differentfrom that of the zirconia contained in the first zirconia layer.

The sintered body of the present embodiment is a so-called layered bodywhich is a composition having a multilayer structure, and is a layeredbody consisting of a sintered structure. In the present embodiment, thesintered structure is a structure mainly made of zirconia in a laterstage of sintering.

The sintered body of the present embodiment has a zirconia layer(hereinafter, also simply referred to as a “zirconia layer”) whichcontains stabilizer-containing zirconia and a colorant. The zirconialayer mainly consists of crystal grains of zirconia containing astabilizer. Accordingly, the sintered body of the present embodiment canalso be regarded as a layered body including two or more layerscontaining a colorant and zirconia consisting of zirconia crystal grainscontaining a stabilizer.

FIG. 1 is a schematic diagram which shows an example of a structure ofthe sintered body of the present embodiment and schematically shows across section of a sintered body (100) having a structure in which twozirconia layers containing stabilizer-containing zirconia and a colorantare layered. In FIG. 1, a direction (hereinafter, also referred to as a“layering direction”) in which layers are piled up is indicated as aY-axis direction, and a direction (hereinafter, also referred to as a“horizontal direction”) in which each layer spreads is indicated as anX-axis direction.

The sintered body (100) includes zirconia layers which are a firstzirconia layer (hereinafter, also referred to as a “first layer”) (11)containing a colorant and zirconia having a stabilizer content ofgreater than or equal to 3.3 mol % and a second zirconia layer(hereinafter, also referred to as a “second layer”) (12) containing acolorant and zirconia having a stabilizer content different from that ofthe zirconia contained in the first zirconia layer. The sintered body(100) is shown as a sintered body having a structure in which the firstlayer (11) and the second layer (12) are layered adjacent to each other.In the case where the sintered body has a structure in which zirconialayers containing zirconia having different stabilizer contents arelayered, the sintered body becomes a layered body in which the change incolor tone based on synergistic effects such as translucency or thedifference in the stabilizer content can be visually recognized. A statein which the first layer comes into contact with the second layer via aninterface is shown in the sintered body (100). However, the layers ofthe sintered body of the present embodiment may be layered in a state inwhich there is no visually recognizable interface, and the interfacebetween layers is not limited to being linear.

In the sintered body (100), the first layer and the second layer havesubstantially the same thickness. However, in the sintered body of thepresent embodiment, each layer may have a different thickness(hereinafter, also referred to as a “layer thickness”), and the layerthickness of either the first layer or the second layer may be thicker.For example, the layer thicknesses of the first layer and the secondlayer may satisfy the following relation, and the layer thickness of azirconia layer having a high stabilizer content is thicker than that ofa zirconia layer having a low stabilizer content. Examples of the layerthickness include 1 mm to 20 mm, 2 mm to 15 mm, and 3 mm to 10 mm.

D _(high) ≥D _(low),preferably 2×D _(low) ≥D _(high) ≥D _(low)

where D_(high) is a layer thickness of a zirconia layer having a highstabilizer content, and D_(low) is a layer thickness of a zirconia layerhaving a low stabilizer content.

The shape of the sintered body of the present embodiment is arbitrary,and may be at least one selected from the group consisting of aspherical shape, an elliptical shape, a disk shape, a cylindrical shape,a cubic shape, a rectangular parallelepiped shape, and a polyhedralshape, or may be a shape suitable for dental materials including dentalprosthetic materials such as a crown, a bridge, and an onlay, or anarbitrary shape according to other intended uses. In the presentembodiment, the spherical shape may include a shape similar to a truesphere such as a substantially spherical shape in addition to a truesphere, and a polyhedral shape may include a shape similar to apolyhedron such as a substantially polyhedral shape in addition to apolyhedron.

The dimensions of the sintered body of the present embodiment arearbitrary, and examples thereof include 10 mm to 120 mm in length, 12 mmto 120 mm in width, and 6 mm to 40 mm in height. In addition, thethickness of the sintered body of the present embodiment in the layeringdirection, that is, the height of the sintered body is arbitrary, andexamples thereof include 4 mm to 40 mm and 5 mm to 30 mm.

The sintered body of the present embodiment is preferably in a state inwhich the first layer and the second layer are layered adjacent to eachother. In addition, the first layer and the second layer are eachpreferably positioned as a lowest layer (hereinafter, also referred toas a “lowermost layer”) in the layering direction or at a topmost layer(hereinafter, also referred to as an “uppermost layer”) in the layeringdirection. It is preferable that one of the first layer and the secondlayer be positioned as a lowermost layer and the other one of the firstlayer and the second layer be positioned as an uppermost layer.

The sintered body of the present embodiment may have a structure inwhich two or more zirconia layers containing stabilizer-containingzirconia and a colorant are layered, or may have a structure in whichthree or more zirconia layers, or four or more zirconia layers arelayered. The sintered body becomes a layered body in which a smallchange in texture can be visually recognized according to increase inthe number of layers. In a case where the same texture as that ofnatural teeth is required, the sintered body of the present embodimentmay have a structure in which 2 to 10 zirconia layers, 2 to 5 zirconialayers, or 2 to 4 zirconia layers are layered, for example.

A zirconia layer (hereinafter, also referred to as an “optional layer”)other than the first layer and the second layer may be a zirconia layercontaining a colorant and zirconia having a stabilizer content of higherthan or equal to a minimum value and lower than or equal to a maximumvalue of the contents of the stabilizers of zirconia contained in thefirst layer and the second layer. The sintered body of the presentembodiment may contain a plurality of optional layers.

Although the layering order of the optional layers is arbitrary, astructure is preferable in which an optional layer is interposed betweenthe first layer and the second layer. In the case where the sinteredbody of the present embodiment includes a plurality of optional layers(an optional layer in a first layer is also referred to as a thirdlayer”, optional layers in a second or higher layers are also referredto as a “fourth layer”, a “fifth layer”, and the like), the sinteredbody preferably has a structure in which the zirconia layers are layeredso that the change in the contents of the stabilizers in the layeringdirection becomes constant, that is, the change increases (ordecreases). The structure in which the optional layers are interposedbetween the first layer and the second layer in the present embodimentis a structure in which the optional layer is positioned between thefirst layer and the second layer in the layering direction, and is notlimited to a structure in which the optional layers are layered directlyadjacent to both the first layer and the second layer. In addition, theordinal numbers such as first, second, and third in the presentembodiment are numbers given for convenience of description, and do notmean a layered state or a permutation such as a layering order.

FIG. 2 is a schematic diagram which shows another example of a structureof the sintered body of the present embodiment and shows a cross sectionof a sintered body (200) having a structure in which three zirconialayers are layered. The sintered body (200) has a structure in which athird layer (23) is layered in addition to a first layer (21) and asecond layer (22) and the third layer (23) is interposed between thefirst layer (21) and the second layer (22).

In a case where the sintered body includes a plurality of zirconialayers such as the fourth layer and the fifth layer, the sintered bodypreferably has a structure in which the zirconia layers are layered sothat the contents of stabilizers change constantly in the layeringdirection. Accordingly, gradations of color tones are formed based onsynergistic effects such as the translucency or the difference in thestabilizer content.

In the sintered body of the present embodiment, a warp (hereinafter,also simply referred to as a “warp”) measured using a thickness gaugeaccording to JIS B 7524:2008 is less than or equal to 1.0 mm. A sinteredbody having a structure with two or more zirconia layers has a shapewarped in the layering direction (or a direction opposite to thelayering direction) through sintering. In a case where such a sinteredbody is disposed on a horizontal plate, a gap is formed between thesintered body and the horizontal plate.

The warp in the present embodiment is a value measured using a thicknessgauge (hereinafter, also simply referred to as a “gauge”) according toJIS B 7524:2008. The warp of the sintered body of the present embodimentis preferably less than or equal to 0.3 mm, more preferably less than orequal to 0.2 mm, still more preferably less than or equal to 0.1 mm, andstill more preferably less than or equal to 0.05 mm. The sintered bodypreferably does not have a warp (warp of 0 mm), but the sintered body ofthe present embodiment may have a warp (warp of greater than or equal to0 mm) to a degree that cannot be measured by a gauge. The sintered bodyof the present embodiment has, for example, a warp greater than 0 mm, orgreater than or equal to 0.01 mm. It is preferable that the warp be lessthan or equal to 0.06 mm, less than or equal to 0.05 mm, or less than orequal to a measurement limit (less than 0.03 mm).

The warp can be measured using a maximum value of the thickness of agauge that can be inserted into a gap formed in a state in which asintered body is disposed so that a convex portion of the sintered bodycomes into contact with a horizontal plate. FIG. 3 is a schematicdiagram showing a method for measuring a warp. A sintered body (300)shows a cross section of a disk-shaped sample and shows a sintered bodywarped in the layering direction (Y-axis direction). In FIG. 3, the warpof the sintered body (300) is emphasized for description. When measuringthe warp, the sintered body (300) with a concave-convex shape isdisposed so that the convex portion of the sintered body comes intocontact with a horizontal plate (31) as shown in FIG. 3. Accordingly, agap is formed between the horizontal plate (31) and a surface(hereinafter, also referred to as a “bottom surface”) on which thesintered body (300) comes into contact with the horizontal plate (31).The warp can be measured by inserting a gauge into the gap and using amaximum value of the thickness of the gauge that can be inserted. FIG. 3shows a state in which a gauge (32A) is positioned under the bottomsurface of the sintered body (300) and can be inserted into the gap. Onthe other hand, FIG. 3 shows a state in which a gauge (32B) is notpositioned under the bottom surface of the sintered body (300) andcannot be inserted into the gap. The gauges (32A) and (32B) in FIG. 3are gauges having different thicknesses by one step (for example, 0.01mm), and the warp of the sintered body (300) becomes the thickness ofthe gauge (32A). In order to simplify the description, FIG. 3 shows adiagram in which both the gauges (32A) and (32B) are inserted into thegap. However, the warp may be measured by inserting gauges sequentiallyfrom a thin gauge (for example, the warp is measured using the gauge(32A) which is then removed, and the warp is subsequently measured usingthe thicker gauge (32B)).

In the sintered body of the present embodiment, the warp (hereinafter,also referred to as a “deformation amount”) with respect to thedimension of the sintered body is preferably less than or equal to 1.0,more preferably less than or equal to 0.5, still more preferably lessthan or equal to 0.2, and still more preferably less than or equal to0.15. The deformation amount is, for example, greater than or equal to0, greater than or equal to 0.01, or greater than or equal to 0.05.

The deformation amount can be obtained from the following equation.

Deformation amount=(warp: mm)/(dimension of sintered body: mm)×100

The dimension of the sintered body is a size of the sintered body in adirection perpendicular to the direction of the warp. The sintered body(300) of FIG. 3 is formed along the layering direction (Y-axisdirection). Therefore, the dimension of the sintered body (300) is asize (33) of the sintered body in the horizontal direction (X-axisdirection) perpendicular to the layering direction. The dimension can bemeasured through a well-known measurement method using calipers, amicrometer, and the like. For example, in a case of a disk-shaped orcylindrical layered body, diameters of upper ends and diameters of lowerends at four points are measured using calipers, and an average value ofthe diameters of the upper ends and the lower ends is obtained to obtainthe dimension of the layered body using the average value of theobtained values.

In the present embodiment, the warp and the deformation amount arepreferably values measured using a disk-shaped sample as a measurementsample and more preferably values measured using a disk-shaped samplehaving a diameter of 5 mm to 120 mm as a measurement sample.

The sintered body of the present embodiment consists of zirconia layerscontaining a colorant and zirconia containing a stabilizer. The zirconialayer is a layer containing zirconia as a main component, and thezirconia is zirconia (hereinafter, also referred to as“stabilizer-containing zirconia”) containing a stabilizer. The sinteredbody and the zirconia layer of the present embodiment may contain notonly a colorant and stabilizer-containing zirconia but also unavoidableimpurities such as hafnia (HfO₂).

In the sintered body of the present embodiment, the zirconia ispreferably zirconia in a state in which zirconia obtained by subjectinga zirconia sol to a heat treatment is sintered, more preferably zirconiain a state in which zirconia obtained by subjecting a zirconia solobtained by hydrolyzing a zirconium compound to a heat treatment issintered, and still more preferably zirconia in a state in whichzirconia obtained by subjecting a zirconia sol obtained by hydrolyzingzirconium oxychloride to a heat treatment is sintered.

Examples of zirconia contained in a zirconia layer include sinteredzirconia, that is, zirconia crystal grains.

A stabilizer may have a function of suppressing phase transition ofzirconia. Examples of the stabilizer include at least any of astabilizer (hereinafter, also referred to as a “non-coloringstabilizer”) which has a function of suppressing phase transition butdoes not contain an element having a function of coloring zirconia, or astabilizer (hereinafter, also referred to as a “coloring stabilizer”)which has functions of suppressing phase transition and coloringzirconia. The stabilizer may be a non-coloring stabilizer or a coloringstabilizer, and preferably includes at least a non-coloring stabilizer.

Specific examples of the stabilizer include one or more selected fromthe group consisting of yttria (Y₂O₃), calcia (CaO), magnesia (MgO),ceria (CeO₂), praseodymium oxide (Pr₆O₁₁), neodymium oxide (Nd₂O₃),terbium oxide (Tb₄O₇), erbium oxide (Er₂O₃), and ytterbium oxide(Yb₂O₃).

Examples of the non-coloring stabilizer include one or more selectedfrom the group consisting of yttria, calcia, magnesia, and ceria. Atleast any of yttria or ceria is preferable and yttria is morepreferable.

Examples of the coloring stabilizer include one or more selected fromthe group consisting of praseodymium oxide, neodymium oxide, terbiumoxide (terbia), erbium oxide (erbia), and ytterbium oxide, and at leastany of terbium oxide or erbium oxide is preferable.

The stabilizer is in a state of being contained and doped(solid-soluted) in zirconia. In addition, the sintered body of thepresent embodiment preferably does not contain an undoped stabilizer,that is, a stabilizer not doped in zirconia. In the present embodiment,the expression “not containing an undoped stabilizer” means that no XRDpeaks derived from a stabilizer can be confirmed in XRD measurement andXRD pattern analysis to be described below. Incorporation of an undopedstabilizer is acceptable as long as no XRD peak derived from thestabilizer can be confirmed.

The stabilizer content (hereinafter, also referred to as a “stabilizercontent of the first layer”) of the stabilizer-containing zirconiacontained in the first layer is higher than or equal to 3.3 mol %,preferably higher than or equal to 3.5 mol %, more preferably higherthan or equal to 3.7 mol %, still more preferably higher than or equalto 4 mol %, still more preferably higher than or equal to 4.1 mol %, andstill more preferably higher than or equal to 4.2 mol %. The stabilizercontent of the first layer is, for example, lower than or equal to 6.0mol %, lower than or equal to 5.8 mol %, lower than or equal to 5.5 mol%, or lower than or equal to 5.0 mol %. The stabilizer content of thefirst layer is, for example, 3.3 mol % to 6.0 mol %, 3.5 mol % to 5.0mol %, 4 mol % to 6.0 mol %, and higher than or equal to 4 mol % andlower than 5.0 mol %.

The content (hereinafter, also referred to as a “stabilizer content of asecond layer”) of a stabilizer of stabilizer-containing zirconiacontained in a second layer may be different from the stabilizer contentof the first layer, but is preferably higher than that of the firstlayer. That is, the sintered body of the present embodiment preferablydoes not contain a zirconia layer in which the content of a stabilizerof zirconia is lower than 3.3 mol %. Accordingly, a sintered bodyexhibiting a color tone closer to that of natural teeth is easilyobtained.

The stabilizer content of the second layer may be higher than or equalto 1.5 mol %, higher than or equal to 2.0 mol %, or higher than or equalto 3.0 mol %, and is preferably higher than or equal to 4.0 mol %, morepreferably higher than 4.0 mol %, still more preferably higher than orequal to 4.5 mol %, still more preferably higher than or equal to 5.0mol %, and still more preferably higher than 5.0 mol %. In addition, thestabilizer content of the second layer is, for example, lower than orequal to 7.0 mol %, lower than or equal to 6.5 mol %, lower than orequal to 6.0 mol %, or lower than or equal to 5.8 mol %. In the casewhere the first layer and the second layer have different contents ofstabilizers and the stabilizer contents of both the layers are withinthese ranges, the sintered body is likely to exhibit a texture that canbe visually recognized as a texture close to that of natural teeth. Thestabilizer content of the second layer is, for example, 1.5 mol % to 7.0mol %, 3.0 mol % to 6.5 mol %, 3.9 mol % to 6.5 mol %, 4.5 mol % to 6.5mol %, 5.0 mol % to 6.5 mol %, or higher than 5.0 mol % and lower thanor equal to 6.0 mol %.

The sintered body of the present embodiment preferably includes at leasta first zirconia layer and a zirconia layer containing zirconia having astabilizer content of higher than or equal to 4.5 mol % or higher thanor equal to 5 mol % and more preferably includes a first zirconia layerand a zirconia layer containing zirconia having a stabilizer content ofhigher than 5 mol %. As another embodiment, the sintered body of thepresent embodiment more preferably has a stabilizer content of a firstlayer of 4.0 mol % to 5.1 mol % and a stabilizer content of a secondlayer of 4.5 mol % to 6.0 mol %. Furthermore, the sintered body of thepresent embodiment still more preferably has a stabilizer content of afirst layer of 3.3 mol % to 4.5 mol % and a stabilizer content of asecond layer of higher than 4.5 mol % and lower than or equal to 5.8 mol%, and still more preferably has a stabilizer content of a first layerof 3.8 mol % to 4.3 mol % and a stabilizer content of a second layer of4.7 mol % to 5.5 mol %.

The content (hereinafter, also referred to as a “stabilizer content ofan optional layer”) of a stabilizer of stabilizer-containing zirconiacontained in an optional layer is higher than or equal to a minimumvalue and lower than or equal to a maximum value of the contents of thestabilizers of the zirconia contained in the first layer and the secondlayer, and is preferably higher than a minimum value and lower than amaximum value of the contents of the stabilizers of the zirconiacontained in the first layer and the second layer. The stabilizercontent of the third layer is, for example, 1.5 mol % to 7.0 mol %, 3.0mol % to 6.5 mol %, or 4.0 mol % to 6.0 mol %. In a case where thecontent of the stabilizer of the zirconia contained in the first layeris 4.0 mol % and the content of the stabilizer of the zirconia containedin the second layer is 6.0 mol %, the content of the stabilizer of thezirconia of the optional layer is, for example, 4.0 mol % to 6.0 mol %and preferably higher than 4.0 mol % and less than 6.0 mol %. In a casewhere the stabilizer content of the optional layer is the same as thatof the first layer or the second layer, a zirconia layer which has thesame stabilizer content as the optional layer and is positioned as theuppermost layer or the lowermost layer may be regarded as the firstlayer or the second layer.

The difference between the stabilizer content of the first layer and thestabilizer content of the second layer is preferably greater than orequal to 0.2 mol %, more preferably greater than or equal to 0.5 mol %,still more preferably greater than or equal to 0.7 mol %, still morepreferably greater than or equal to 1.0 mol %, and still more preferablygreater than or equal to 1.2 mol %. As the difference in the stabilizercontent increases, the difference in color tone between the zirconialayers tends to increase, and in contrast, the warp sometimes increases.In a case where the difference between the stabilizer content of thefirst layer and the stabilizer content of the second layer is less than2.5 mol %, or less than or equal to 2.0 mol %, or less than or equal to1.7 mol %, the sintered body is tended to have the same change in colortone as that of natural teeth. It is more preferable that the differencebetween the stabilizer content of the first layer and the stabilizercontent of the second layer be greater than or equal to 0.7 mol % andless than 2.5 mol % and the warp be less than or equal to 0.5 mm.

The sintered body of the present embodiment preferably has a structurein which the difference in the stabilizer content between zirconialayers layered adjacent to each other is 0.5 mol % to 3.0 mol %, 1.0 mol% to 2.5 mol %, or 1.2 mol % to 2.0 mol %.

The stabilizer content (stabilizer content as the entirety of thesintered body) of the sintered body of the present embodiment isarbitrary, but examples thereof include higher than 1.5 mol % and lowerthan 7.0 mol %, 2.5 mol % to 6.5 mol %, 3.0 mol % to 6.0 mol %, or 3.5mol % to 5.8 mol %, and is preferably 4.1 mol % to 5.5 mol % morepreferably 4.2 mol % to 5.0 mol %, and still more preferably 4.2 mol %to 4.8 mol %. The stabilizer content of a sintered body is obtained fromthe following expression and varies depending on the thickness of eachzirconia layer.

Stabilizer content of sintered body=(layer thickness of firstlayer/height of sintered body)×stabilizer content of first layer+(layerthickness of second layer/height of sintered body)×stabilizer content ofsecond layer+ . . . +(layer thickness of n-th layer/height of sinteredbody)×stabilizer content of n-th layer

The stabilizer content of a first layer is higher than or equal to 3.3mol %. Therefore, in a case where the stabilizer content of a secondlayer is, for example, higher than 3.3 mol %, the stabilizer content ofa sintered body including two zirconia layers having the same layerthickness exceeds 3.3 mol %.

In the sintered body of the present embodiment, it is preferable thatthe stabilizer content of a first layer be 3.3 mol % to 5.0 mol %, thestabilizer content of a second layer be 4.6 mol % to 6.0 mol %, and thedifference between the stabilizer content of the first layer and thestabilizer content of the second layer be 0.7 mol % to 1.8 mol %, and itis more preferable that the yttria content of a first layer be 3.8 mol %to 4.5 mol %, the yttria content of a second layer be higher than 5.0mol % and lower than or equal to 5.5 mol %, and the difference betweenthe yttria content of the first layer and the yttria content of thesecond layer be 1.0 mol % to 1.6 mol %.

The stabilizer content in the present embodiment is a molar ratio of astabilizer to the total amount of zirconia and the stabilizer. Whencalculating the stabilizer content, the content of each stabilizer maybe obtained in terms of an oxide as described above. In a case where,for example, yttria and erbia are contained as stabilizers, thestabilizer content (mol %) is obtained from(Y₂O₃+Er₂O₃)/(ZrO₂+Y₂O₃+Er₂O₃)×100.

The colorant in the present embodiment is an element having a functionof coloring zirconia. Specific examples of the colorant include at leastany of a transition metal element and a lanthanoid-based rare earthelement, and are preferably one or more selected from the groupconsisting of iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn),praseodymium (Pr), neodymium (Nd), europium (Eu), gadolinium (Gd),terbium (Tb), erbium (Er), and ytterbium (Yb), more preferably one ormore selected from the group consisting of iron, cobalt, manganese,praseodymium, gadolinium, terbium, and erbium, and still more preferablyone or more selected from the group consisting of iron, cobalt, terbium,and erbium.

The colorant contained in the sintered body of the present embodimentmay be at least any of a colorant (hereinafter, also referred to as an“oxide colorant”) contained in a state of oxide or a colorant, such as acoloring stabilizer, contained in a state of being doped in zirconia.Examples of preferred oxide colorants include one or more selected fromthe group consisting of iron, cobalt, nickel, and manganese, and atleast any of iron or cobalt is more preferable. The sintered body of thepresent embodiment may contain two or more colorants, or may contain,for example, two to five types of colorants or three to four types ofcolorants. The sintered body of the present embodiment preferablycontains at least a coloring stabilizer, more preferably contains atleast any of terbium or erbium, and still more preferably contains atleast terbium and erbium.

The types and the contents of colorants contained in zirconia layers areequal to each other. For this reason, it is unnecessary to change thecontent of a colorant in each layer when producing a sintered body. Inaddition, since the types of colorants contained therein are equal toeach other, natural color tone changes such as gradations of similarcolors can be obtained by the sintered body. The “contents of colorantsbeing equal” in the present embodiment means that the contents ofcolorants between layers are equal to each other to a degree that theeffect of the layered body of the present embodiment can be exhibited. Adifference in the colorant content is acceptable which imparts a changein color tone to a sintered body but does not cause a difference in asintering behavior derived from the difference in the colorant contentbetween layers in a process of producing the layered body.

The colorant content of the sintered body of the present embodiment is,as a mass ratio of a colorant in terms of an oxide with respect to themass of the sintered body of the present embodiment, higher than 0 wt %and lower than or equal to 1.5 wt %, preferably 0.01 wt % to 1.0 wt %,more preferably 0.03 wt % to 0.8 wt %, and still more preferably 0.04 wt% to 0.3 wt %. For example, in a case where yttria (non-coloringstabilizer) and erbia (coloring stabilizer) are contained asstabilizers, and alumina and cobalt (oxide colorant) are contained, thecontent (wt %) of the colorant is obtained from(Co₃O₄+Er₂O₃)/(ZrO₂+Y₂O₃+Er₂O₃+Co₃O₄+Al₂O₃)×100. In terms of an oxide ofthe colorant, praseodymium oxide may be Pr₆O₁₁, neodymium oxide may beNd₂O₃, terbium oxide may be Tb₄O₇, erbium oxide may be Er₂O₃, andytterbium oxide may be Yb₂O₃, iron may be Fe₂O₃, cobalt may be Co₃O₄,nickel may be NiO, and manganese may be Mn₃O₄.

Each zirconia layer has an equal colorant content. For this reason, thecontent of a colorant contained in each zirconia layer, that is the massratio of a colorant contained in each zirconia layer in terms of anoxide with respect to the mass of each zirconia layer becomes equal tothe colorant content of the above-described sintered body.

The sintered body of the present embodiment may contain alumina, and atleast one zirconia layer preferably contains zirconia. The aluminacontent of the sintered body of the present embodiment may be, as aratio of the weight of alumina to the weight of the sintered body, forexample, higher than or equal to 0 wt %, 0 wt % to 0.15 wt %, 0 wt % to0.10 wt %, or 0 wt % to 0.07 wt %. In the case where alumina iscontained, the alumina content is, for example, higher than 0 wt % andlower than or equal to 0.15 wt %, preferably 0.005 wt % to 0.10 wt %,and more preferably 0.01 wt % to 0.70 wt %.

The alumina content of each zirconia layer is, for example, within thesame range as described above. In some cases, the alumina content ofeach zirconia layer affects a thermal shrinkage behavior in acalcination stage. The alumina content of each zirconia layer isarbitrary. Each zirconia layer may have a different alumina content, butthey preferably have the same alumina content. In the case wherezirconia layers have a different alumina content, the difference in thealumina content of adjacent zirconia layers is, for example, higher than0 wt % and lower than or equal to 1.0 wt %, greater than 0 wt % andlower than or equal to 0.5 wt %, greater than 0 wt % and lower than orequal to 0.03 wt %, or 0.005 wt % to 0.01 wt %. In a case of a zirconialayer made of zirconia which contains alumina (Al₂O₃) and of which anon-coloring stabilizer is yttria (Y₂O₃) and a coloring stabilizer iserbia (Er₂O₃), the alumina content can be obtained by{Al₂O₃/(ZrO₂+Y₂O₃+Er₂O₃+Al₂O₃)}×100 (wt %).

It is preferable that the sintered body of the present embodiment do notsubstantially contain any of silica (SiO₂) or titania (TiO₂).

The sintered body of the present embodiment preferably contains azirconia layer containing zirconia of which a crystal phase is at leastone of a tetragonal crystal (T phase) or a cubic crystal (C phase), morepreferably contains zirconia layer containing zirconia having at least atetragonal crystal as a main phase, and still more preferably contains azirconia layer containing zirconia having a tetragonal crystal as a mainphase and a zirconia layer containing zirconia having a cubic crystal asa main phase. The “main phase” in the present embodiment means a crystalphase having a largest existence proportion (proportion of an integratedintensity of a peak) in crystal phases of zirconia. The abundance ratiocan be obtained from an XRD pattern of the surface of the sintered body.

The following conditions can be exemplified as conditions for measuringthe XRD pattern of the surface of the sintered body.

Source: CuK α-rays (λ=1.541862 Å)

Measurement mode: step and scan

Scan condition: 0.000278° per second

Measurement range: 2θ=10-140°

Irradiation width: constant (10 mm)

The obtained XRD pattern is subjected to Rietveld analysis, and theratio (proportion of an integrated intensity of a peak) of a tetragonalcrystal and a cubic crystal is obtained. The crystal phase with ahighest proportion may be regarded as a main phase. The measurement ofan XRD pattern and the Rietveld analysis can be performed using ageneral-purpose powder X-ray diffractometer (for example, X'pert PRO MPDmanufactured by Spectris Co., Ltd.) and analysis software (for example,RIETAN-2000).

The density of the sintered body of the present embodiment which ismeasured through a method according to JIS R 1634 is, for example, 5.7g/cm³ to 6.3 g/cm³ and preferably 5.9 g/cm³ to 6.1 g/cm³. The density inthese ranges is a density which corresponds to a relative density ofgreater than or equal to 99%, and such density is a density of thesintered body having a practical strength, that is, the dense sinteredbody.

As color tones of the sintered body of the present embodiment and thezirconia layers, the brightness L* represented by a L*a*b* color systemis 60 to 90 and preferably 76.5 to 85, the hue a* is −5 to 15 andpreferably −3 to 10, and the hue b* is 0 to 45 and preferably 3 to 35,for example. In the case where the color tone is within these ranges,the sintered body exhibits a color tone similar to that of naturalteeth.

Since the sintered body of the present embodiment has a change in colortone, the chroma C* of an uppermost layer is preferably different fromthat of a lowermost layer. The chroma C* is an index indicatingvividness and is obtained by C*={(a*)²+(b*)²}^(0.5) in which the hue a*and b* is represented by the L*a*b* color system. An absolute value(ΔC*) of the difference in the chroma C* between the uppermost layer andthe lowermost layer is, for example, 0.1 to 15.0, 0.3 to 10.0, 1.0 to5.0, or 1.5 to 3.0. In the case where ΔC* is within these ranges, thelayered body can be visually recognized as one having gradations ofvividness close to natural teeth. Similarly, an absolute value (ΔL*) ofthe difference in the brightness L* between the uppermost layer and thelowermost layer is, for example, 1.0 to 15.0 or 1.5 to 5.0.

The color tones (L*, a*, and b*) and C* can be obtained using valuesmeasured through an SCI method using a spectrocolorimeter including alighting/light-receiving optical system according to geometricconditions c of JIS Z 8722. Examples of the spectrocolorimeter includeCM-700d manufactured by Konica Minolta, Inc. Examples of specificmeasurement conditions of the color tones and C* in a method (so-calledblack background measurement) for placing a measurement sample on ablack plate for the measurement include the following conditions.

Light source: light source D65

View angle: 10°

Measurement method: SCI

The sintered body of the present embodiment preferably contains at leasta zirconia layer having translucency. Furthermore, the sintered body ofthe present embodiment preferably has a zirconia layer having a totallight transmittance (hereinafter, also simply referred to as a “totallight transmittance”) with respect to a CIE standard light source D65 ata sample thickness of 1.0 mm is 30% to 50%, 32% to 45%, or 35% to 42%.In the sintered body of the present embodiment, the wavelength of lightto be absorbed differs depending on its coloration. For this reason, thetotal light transmittance with respect to light, such as the CIEstandard light source D65 which contains different wavelengths, issuitable as an index of the translucency.

The difference in the total light transmittance between zirconia layerslayered adjacent to each other in the sintered body of the presentembodiment is preferably 1% to 10% and more preferably 1.5% to 5%.

The total light transmittance of the sintered body of the presentembodiment is preferably 30% to 50%, 32% to 45%, or 35% to 42%. Thetotal light transmittance of the sintered body of the present embodimentmay be measured by cutting an arbitrary portion of the sintered body inthe horizontal direction and using the cut portion as a measurementsample obtained by processing the cut portion so as to have a samplethickness of 1 mm.

The total light transmittance can be measured through a method accordingto JIS K 7361 and can be obtained as a transmittance value obtainedusing a CIE standard light source D65 as incident light and by totalingdiffuse transmittance and linear transmittance with respect to theincident light. A sample with a thickness of 1 mm and a surfaceroughness (Ra) of less than or equal to 0.02 μm is used as a measurementsample and is irradiated with light of a CIE standard light source D65using a general turbidimeter (a haze meter; for example, NDH2000manufactured by NIPPON DENSHOKU INDUSTRIES Co., LTD.) The transmittance(diffuse transmittance and linear transmittance) of the sample may bemeasured by condensing transmitted light using an integrating sphere andmay be used as a total light transmittance.

In the sintered body of the present embodiment, a three-point bendingstrength measured through a method according to JSI R 1601 is preferablygreater than or equal to 500 MPa, more preferably greater than or equalto 550 MPa, and still more preferably greater than or equal to 600 MPa.Examples of the three-point bending strength includes less than 1,100MPa and less than or equal to 1,000 MPa.

FIG. 4 is a schematic diagram showing a state of measuring a three-pointbending strength of a sintered body (400) consisting of two zirconialayers. The sintered body (400) is shown as a sintered body having astructure in which two zirconia layers have different layer thicknesses.In FIG. 4, a layering direction is shown in an X-axis direction and ahorizontal direction is shown in a Y-axis direction. A measurementsample to be used for measuring the three-point bending strength is arectangular parallelepiped sintered body produced while setting thewidth and the thickness in the layering direction and the length in thehorizontal direction. The dimension of the measurement sample is 4 mm inwidth, 3 mm in thickness, and 45 mm in length. As shown in FIG. 4, thethree-point bending strength may be measured by applying a load (41) tothe measurement sample (400) so as to be perpendicular to the length ofthe measurement sample. The measurement sample may be disposed so thatthe load (41) is applied at the middle of a fulcrum points distance(42). The fulcrum points distance is 30 mm.

Next, main points different from the above-described sintered body willbe described with reference to an embodiment in which the layered bodyis a calcined body.

The calcined body of the present embodiment is a calcined body which hasa structure, in which two or more zirconia composition layers containinga colorant and zirconia which contains a stabilizer and has a neckingstructure, and in which types and contents of the colorants contained inthe zirconia composition layers are equal to each other, and includes atleast: a first zirconia composition layer containing a colorant andzirconia which has a stabilizer content of higher than or equal to 3.3mol %; and a second zirconia composition layer containing a colorant andzirconia having a stabilizer content different from that of the zirconiacontained in the first zirconia composition layer.

The calcined body is a so-called layered body which is a compositionhaving a multilayer structure, and is a layered body consisting ofso-called calcined particles which are structures having a neckingstructure. The calcined body can be processed as necessary to be used asa precursor of a sintered body, and is also called a pre-sintered body,soft-sintered body or a semi-sintered body.

The necking structure is a structure of zirconia subjected to a heattreatment at a temperature lower than a sintering temperature, and is astructure in which zirconia particles chemically adhere to each other.As shown in FIG. 5, a part of the particle shape of zirconia (51), whichis contained in the zirconia composition layers of the calcined body, ina powder composition can be checked from the zirconia (51). In thepresent embodiment, the structure having a necking structure is astructure made of zirconia in an initial stage of sintering. Thisstructure having a necking structure is different from the sinteredstructure, that is, the structure consisting of zirconia crystal grainsin a later stage of sintering. Accordingly, the calcined body of thepresent embodiment can also be regarded as a layered body including twoor more layers containing a colorant and zirconia which contains astabilizer, has a necking structure, and is consisting of zirconiaparticles.

The calcined body has, instead of zirconia layers, zirconia compositionlayers (hereinafter, also referred to as “composition layers”)containing a colorant and zirconia which contains a stabilizer and has anecking structure, and has the same structure as the layered structureshown in FIG. 1 or 2. The stabilizer and the colorant in the calcinedbody may doped in zirconia or may be in a state of an oxide or aprecursor thereof.

In the calcined body, a warp is preferably less than or equal to 1.0 mm,more preferably less than or equal to 0.5 mm, still more preferably lessthan or equal to 0.3 mm, still more preferably less than or equal to 0.2mm, still more preferably less than or equal to 0.1 mm, and still morepreferably less than or equal to 0.05 mm. The calcined body preferablydoes not have a warp (warp of 0 mm), but may have a warp (warp ofgreater than or equal to 0 mm) to a degree that cannot be measured by agauge. The calcined body has, for example, a warp greater than 0 mm, orgreater than or equal to 0.01 mm. It is preferable that the warp be lessthan or equal to 0.06 mm, less than or equal to 0.05 mm, or less than orequal to a measurement limit (less than 0.03 mm). In the calcined body,the deformation amount is preferably less than or equal to 1.0, morepreferably less than or equal to 0.5, still more preferably less than orequal to 0.2, and still more preferably less than or equal to 0.15. Thedeformation amount is, for example, greater than or equal to 0, greaterthan or equal to 0.01, or greater than or equal to 0.05.

Zirconia contained in the calcined body is preferably in a state inwhich zirconia obtained by subjecting a zirconia sol to a heat treatmentis heat-treated at a temperature lower than a sintering temperature,more preferably in a state in which zirconia obtained by subjecting azirconia sol obtained by hydrolyzing a zirconium compound to a heattreatment is heat-treated at a temperature lower than a sinteringtemperature, and still more preferably in a state in which zirconiaobtained by subjecting a zirconia sol obtained by hydrolyzing zirconiumoxychloride to a heat treatment is heat-treated at a temperature lowerthan a sintering temperature.

The stabilizer content of stabilizer-containing zirconia contained in afirst composition layer (hereinafter, also referred to as a “firstcomposition layer”), the stabilizer content of stabilizer-containingzirconia contained in a second composition layer (hereinafter, alsoreferred to as a “second composition layer”), and the stabilizer contentof stabilizer-containing zirconia contained in an optional compositionlayer (hereinafter, also referred to as an “optional composition layer”)may be the same as those of the first layer, the second layer, and theoptional layer, respectively.

The stabilizer contents of the calcined body and each composition layerare arbitrary, but may be the same as those of the sintered body of thepresent embodiment described above.

The calcined body more preferably contains a zirconia composition layercontaining zirconia having at least a tetragonal crystal or a cubiccrystal as a main phase.

The density of the calcined body is, for example, 2.4 g/cm³ to 3.7 g/cm³and preferably 3.1 g/cm³ to 3.5 g/cm³. The density in these rangescorresponds to a relative density of 40% to 60%. The calcined body maybe a layered body having a strength suitable for processing such asCAD/CAM processing.

The density of the calcined body is obtained from a weight obtained byweight measurement and a volume obtained by dimensional measurement.

The color tones of the zirconia layers contained in the calcined bodymay be different from those of a sintered body obtained by sintering thecalcined body, or may not have a change in color tone.

The calcined body and each composition layer are opaque and have a totallight transmittance of 0%. In consideration of a measurement error, thetotal light transmittance is, for example, 0% to 0.2%.

The calcined body may have such a strength that a defect is less likelyto occur during processing such as CAD/CAM or cutting.

The layered body of the present embodiment can be used for well-knownzirconia applications such as decorative members, structural materialsor optical materials. In the case where the layered body is a sinteredbody, it can be suitably used as dental materials such as dentures, forexample, a crown and a bridge and can be used as dental materialscontaining the sintered body of the present embodiment. In addition, inthe case where the layered body is a calcined body, it can be suitablyused as precursors of dental materials such as dentures, for example, acrown and a bridge, and can be used as dental prosthetic materials suchas a blank, a disc, a block, and a mill blank, and precursors thereof.Furthermore, the layered body can be provided as dental materialscontaining the layered body of the present embodiment.

Next, a method for producing a layered body of the present embodimentwill be described.

A production method in an aspect in which the layered body of thepresent embodiment is a sintered body is a method for producing alayered body, the method including: a step of sintering a green body at1,200° C. to 1,600° C.,

wherein the green body which has a structure, in which two or morepowder composition layers consisting of a powder composition containinga stabilizer-containing zirconia, a colorant, and a binding agent arelayered, and in which types and contents of the colorants contained inthe powder composition layers are equal to each other,

includes at least a first powder composition layer containing a bindingagent, a colorant, and zirconia which has a stabilizer content of higherthan or equal to 3.3 mol % and a second powder composition layercontaining a binding agent, a colorant, and zirconia which has astabilizer content different from that of the zirconia contained in thefirst powder composition layer, and

has a difference in a binding agent content between the first powdercomposition layer and the second powder composition layer exceeds 0.01wt %.

In addition, another production method of the present embodiment is amethod for producing a layered body, the method including: a step ofcalcining a green body at a temperature of is higher than or equal to800° C. and lower than 1,200° C. to obtain a calcined body;

and a step of sintering the calcined body at 1,200° C. to 1,600° C.,

wherein the green body which has a structure, in which two or morepowder composition layers consisting of a powder composition containinga stabilizer-containing zirconia, a colorant, and a binding agent arelayered, and in which types and contents of the colorants contained inthe powder composition layers are equal to each other,

includes at least a first powder composition layer containing a bindingagent, a colorant, and zirconia which has a stabilizer content of higherthan or equal to 3.3 mol % and a second powder composition layercontaining a binding agent, a colorant, and zirconia which has astabilizer content different from that of the zirconia contained in thefirst powder composition layer, and

has a difference in a binding agent content between the first powdercomposition layer and the second powder composition layer exceeds 0.01wt %.

In addition, still another production method of the present embodimentis a method for producing a layered body, the method including a step ofsintering a calcined body at 1,200° C. to 1,600° C. in which thecalcined body which has a structure, in which two or more zirconiacomposition layers containing a colorant and zirconia which contains astabilizer and has a necking structure, and in which types and contentsof the colorants contained in the zirconia composition layers are equalto each other includes at least: a first zirconia composition layercontaining a colorant and zirconia which has a stabilizer content ofhigher than or equal to 3.3 mol %; and a second zirconia compositionlayer containing a colorant and zirconia having a stabilizer contentdifferent from that of the zirconia contained in the first zirconiacomposition layer.

A production method in an aspect in which the layered body of thepresent embodiment is a calcined body is a method for producing alayered body, the method including: a step of calcining a green body ata temperature of higher than or equal to 800° C. and lower than 1,200°C.,

wherein the green body which has a structure, in which two or morepowder composition layers consisting of a powder composition containinga stabilizer-containing zirconia, a colorant, and a binding agent arelayered, and in which types and contents of the colorants contained inthe powder composition layers are equal to each other,

includes at least a first powder composition layer containing a bindingagent, a colorant, and zirconia which has a stabilizer content of higherthan or equal to 3.3 mol % and a second powder composition layercontaining a binding agent, a colorant, and zirconia which has astabilizer content different from that of the zirconia contained in thefirst powder composition layer, and

has a difference in a binding agent content between the first powdercomposition layer and the second powder composition layer exceeds 0.01wt %.

The green body used for the production method of the present embodimentis a green body has a structure, in which two or more powder compositionlayers consisting of a powder composition containing astabilizer-containing zirconia, a colorant, and a binding agent arelayered, and in which types and contents of the colorants contained inthe powder composition layers are equal to each other, and includes atleast a first powder composition layer containing a binding agent, acolorant, and zirconia which has a stabilizer content of higher than orequal to 3.3 mol % and a second powder composition layer containing abinding agent, a colorant, and zirconia which has a stabilizer contentdifferent from that of the zirconia contained in the first powdercomposition layer, and has a difference in a binding agent contentbetween the first powder composition layer and the second powdercomposition layer exceeds 0.01 wt %.

It is known that a powder composition containing a binding agentimproves the cohesive strength of zirconia and suppresses defects, suchas cracks or chips, during molding. In general, it is necessary to makethe content of a binding agent in a powder composition which is used forproducing a green body uniform in order to make the strength of theobtained green body uniform. On the other hand, it is considered thatthe binding agent in the green body of the present embodiment not onlyimproves the strength of the green body but also has a function ofsuppresses a generation of stress between layered layers, by differingthe binding agent contents between the layers. Such function isconsidered as different than a function known in prior art As a result,it is considered that deformation during molding is suppressed and thegreen body consisting of a layered body in which powder compositionscontaining zirconia having different stabilizer contents are layered canbe heat-treated without causing excessive defects.

Hereinafter, main points of the green body used for the productionmethod of the present embodiment which are different from those of theabove-described sintered body will be described.

The green body used for the production method of the present embodimentis a green body has a structure, in which two or more powder compositionlayers consisting of a powder composition containing astabilizer-containing zirconia, a colorant, and a binding agent arelayered, and in which types and contents of the colorants contained inthe powder composition layers are equal to each other,

includes at least a first powder composition layer containing a bindingagent, a colorant, and zirconia which has a stabilizer content of higherthan or equal to 3.3 mol % and a second powder composition layercontaining a binding agent, a colorant, and zirconia which has astabilizer content different from that of the zirconia contained in thefirst powder composition layer, and

has a difference in a binding agent content between the first powdercomposition layer and the second powder composition layer exceeds 0.01wt %.

The green body is a so-called layered body which is a composition havinga multilayer structure, and is a layered body consisting of a powdercomposition. The green body can be used as a precursor of a calcinedbody or a sintered body.

The green body has, instead of zirconia layers, powder compositionlayers (hereinafter, also referred to as “powder layers”) consisting ofa powder composition containing stabilizer-containing zirconia, acolorant, and a binding agent, and has the same structure as the layeredstructure shown in FIG. 1 or 2. Accordingly, the green body can also beregarded as a layered body including two or more layers containing abinding agent and powder of stabilizer-containing zirconia. Thestabilizer and the colorant in the green body may be doped in zirconiaor may be in a state of an oxide or a precursor thereof. Examples of theprecursor include one or more selected from the group consisting ofsulfide, chloride, nitrate, sulfate, hydroxide, and oxyhydroxide or oneor more selected from the group consisting of chloride, hydroxide, andoxyhydroxide. In addition, the colorant preferably contains at least anoxide.

In the green body, a warp is preferably less than or equal to 1.0 mm,more preferably less than or equal to 0.3 mm, still more preferably lessthan or equal to 0.2 mm, still more preferably less than or equal to 0.1mm, and still more preferably less than or equal to 0.05 mm. The greenbody preferably does not have a warp (warp of 0 mm), but may have a warp(warp of greater than or equal to 0 mm) to a degree that cannot bemeasured by a gauge. The green body has, for example, a warp greaterthan 0 mm or greater than or equal to 0.01 mm. It is preferable that thewarp be less than or equal to 0.06 mm, less than or equal to 0.05 mm, orless than or equal to a measurement limit (less than 0.03 mm).

In the green body, the deformation amount is preferably less than orequal to 1.0, more preferably less than or equal to 0.5, still morepreferably less than or equal to 0.2, and still more preferably lessthan or equal to 0.15. The deformation amount is, for example, greaterthan or equal to 0, greater than or equal to 0.01, or greater than orequal to 0.05.

Zirconia contained in the powder layers is preferably zirconia obtainedby subjecting a zirconia sol to a heat treatment, more preferablyzirconia obtained by subjecting a zirconia sol obtained by hydrolyzing azirconium compound to a heat treatment, and still more preferablyzirconia obtained by subjecting a zirconia sol obtained by hydrolyzingzirconium oxychloride to a heat treatment.

The zirconia contained in the powder layers preferably zirconia powder.The zirconia powder preferably has an average particle size of 0.3 μm to0.7 μm and 0.4 μm to 0.5 μm.

The colorant contained in the powder layers is preferably in at leastany of a state of being mixed with zirconia powder or a state of beingdoped in zirconia. In addition, colorant powder and zirconia powder maybe mixed with each other.

The binding agent contained in the powder layers is preferably a bindingagent that vaporizes at a temperature lower than or equal to 1,200° C.,more preferably an organic binding agent, and still more preferably anorganic binding agent having fluidity at room temperature (for example,10° C. to 30° C.). In addition, the binding agent may contain aplasticizer or a releasing agent. The organic binding agent is one ormore selected from the group consisting of polyvinyl alcohol, polyvinylbutyrate, wax, and an acrylic resin, preferably one or more of polyvinylalcohol and an acrylic resin, and more preferably an acrylic resin. Theacrylic resin in the present embodiment is a polymer containing at leastany of an acrylic ester or a methacrylic ester. The acrylic resincontained in a powder composition may be used as a binding agent forceramics. Specific examples of acrylic resins include one or moreselected from the group consisting of polyacrylic acid, polymethacrylicacid, an acrylic acid copolymer, and a methacrylic acid copolymer, andderivatives thereof.

The stabilizer content of stabilizer-containing zirconia contained in afirst powder layer, the stabilizer content of stabilizer-containingzirconia contained in a second powder layer, and the stabilizer contentof stabilizer-containing zirconia contained in an optional powder layermay be the same as those of the first layer, the second layer, and theoptional layer, respectively.

The stabilizer contents and the colorant contents of the green body andeach powder layer are arbitrary, but may be the same as those of thesintered body of the present embodiment described above.

From the viewpoint of suppressing defects during molding, the bindingagent content of each powder layer is preferably greater than or equalto 1.5 wt %, more preferably 1.5 wt % to 8.0 wt %, still more preferably2.0 wt % to 6.0 wt %, and still more preferably 2.5 wt % to 5.5 wt %.

In the green body, the difference in the binding agent content(hereinafter, also referred to as a “difference in the amount of thebinding agent”) between the first powder layer and the second powderlayer exceeds 0.01 wt %, and is preferably greater than or equal to 0.03wt %. In this manner, the first powder layer and the second powder layerof the green body have different binding agent contents. Accordingly,generation of stress during molding is suppressed. From the viewpoint ofsuppressing the generation of stress, examples of the difference in theamount of the binding agent include greater than 0.01 wt % and less thanor equal to 5 wt %, or 0.03 wt % to 3.5 wt %, and are preferably 0.04 wt% to 3 wt %, more preferably 0.05 wt % to 2 wt %, still more preferably0.06 wt % to 1.5 wt %, and still more preferably 0.07 wt % to 1 wt %. Inanother embodiment, examples of the difference in the amount of thebinding agent include 0.01 wt % to 0.5 wt %, 0.02 wt % to 0.3 wt %, and0.03 wt % to 0.1 wt %.

The binding agent content is a ratio of the weight of the binding agentto the weight of a powder composition in a powder layer excluding thebinding agent ({binding agent/(powder composition−binding agent)}×100).When producing the powder composition, the total mass of components (forexample, a stabilizer, zirconia, and alumina in terms of an oxide) ofthe powder composition other than the binding agent is obtained, andthen, the mass ratio of the target binding agent with respect to theobtained total mass is obtained to produce the powder composition, forexample.

In order to suppress a warp of the green body, it is preferable toadjust the binding agent content in each powder layer according to thestabilizer contents of adjacent powder layers. Examples of the firstpowder layer and the second powder layer include any case that

the contents of a stabilizer and a binding agent in the second powderlayer are higher than those in the first powder layer,

the contents of a stabilizer and a binding agent in the second powderlayer are lower than those in the first powder layer

the content of a stabilizer in the second powder layer is higher thanthat in the first powder layer and the content of a binding agent in thesecond powder layer is lower than that in the first powder layer, or

the content of a stabilizer in the second powder layer is lower thanthat in the first powder layer and the content of a binding agent in thesecond powder layer is higher than that in the first powder layer.

The first powder layer and the second powder layer are preferably anycase that

the content of a stabilizer in the second powder layer is higher thanthat in the first powder layer and the content of a binding agent in thesecond powder layer is lower than that in the first powder layer, or

the content of a stabilizer in the second powder layer is lower thanthat in the first powder layer and the content of a binding agent in thesecond powder layer is higher than that in the first powder layer. Thecontents of a stabilizer and a binding agent between the first powderlayer and the second powder layer may be different from each other. Itis preferable that the difference in the amount of the binding agent belarge since this tends to cause suppression of a warp of the green body.In addition, it is preferable that one of the first powder layer and thesecond powder layer have a lower stabilizer content and a higher bindingagent content than the other powder layer.

In addition, it is preferable that one powder layer containing zirconiahaving a low stabilizer content in powder layers layered adjacent toeach other have higher binding agent content than the other powderlayer.

On the other hand, in a case where zirconia contained in any one ofpowder layers layered adjacent to each other is zirconia in which two ormore zirconia compounds having different stabilizer contents are mixedwith each other, one powder layer containing zirconia having a lowstabilizer content preferably has a lower binding agent content than theother powder layer.

From the viewpoint of operability, a powder composition contained in apowder layer is preferably powder (hereinafter, also referred to as“granulated powder”) in a state in which zirconia powder, a colorant,and a binding agent are granulated and more preferably granulated powder(hereinafter, also referred to as “powder granules”) granulated intogranules through spray-drying or the like.

The particle size of granulated powder is arbitrary. Examples of averageaggregation sizes include 1 μm to 150 μm, preferably 1 μm to 100 μm,more preferably 5 μm to 50 μm, and still more preferably 5 μm to 30 μm.20 μm to 50 μm can be exemplified as another embodiment.

The average aggregation size in the present embodiment is a sizecorresponding to cumulative 50% in volume particle size distributionmeasurement. The volume particle size distribution is a value that canbe measured using a general-purpose device (for example, MT3100IImanufactured by MicrotracBEL Corp.) and is a volume size of a particleapproximated to a sphere.

The green body more preferably contains a powder layer containingzirconia having at least a tetragonal crystal or a cubic crystal as amain phase.

The density of the green body is, for example, 2.4 g/cm³ to 3.7 g/cm³and preferably 3.1 g/cm³ to 3.5 g/cm³. The density in these rangescorresponds to a relative density of 40% to 60%.

The density of the green body is obtained from a weight obtained byweight measurement and a volume obtained by dimensional measurement.

The color tones of the zirconia layers contained in the green body maybe different from those of a sintered body obtained by sintering thecalcined body, or may not have a change in color tone.

The green body and each powder layer are opaque and has a total lighttransmittance of 0%. In consideration of a measurement error, the totallight transmittance is, for example, 0% to 0.2%.

The green body may have such a strength that cracks or chips are notcaused when used during calcination or sintering.

The green body is obtained by layering powder compositions and moldingthe layered powder compositions. Each powder composition is obtained bymixing zirconia powder with a binding agent at an arbitrary desiredratio through a well-known method. The molding is preferablypress-molding. For example, a molding die is filled with a powdercomposition having a composition corresponding to a lowermost layer toobtain the lowermost layer. Thereafter, the molding die is filled with apowder composition having a composition corresponding to a compositionof a layer adjacent to the lowermost layer, on the lowermost layer. In acase of obtaining a green body having a structure in which three or morepowder layers are layered, the same operation may be repeated to layernecessary powder compositions. After filling the molding die with apowder composition having a composition corresponding to a compositionof an uppermost layer, a preliminary green body is obtained byperforming uniaxial pressing at an arbitrary pressure. A green body isobtained by subjecting the obtained preliminary green body to coldisostatic pressing (hereinafter, also referred to as “CIP”) processing.At the time of layering, it is unnecessary to apply vibration, such asvibration using a vibrator, for forming a mixed layer between layers. Inaddition, the uniaxial pressing is preferably performed after thefilling of the molding die with a powder composition having acomposition corresponding to the uppermost layer, and the pressing ispreferably not performed before filling the molding die with a powdercomposition having a composition corresponding to the uppermost layer.

The molding pressure of the uniaxial pressing is preferably 15 MPa to200 MPa and more preferably 18 MPa to 100 MPa. A warp of a green bodytends to be suppressed as the molding pressure of the uniaxial pressingincreases. As the pressure of the CIP processing, the molding pressureis, for example, 98 MPa to 392 MPa.

The green body becomes a calcined body by processing the green body at atemperature lower than a sintering temperature. Well-known methods canbe used for the calcination method and the calcination conditions.

The holding temperature (hereinafter, also referred to as a “calcinationtemperature”) during calcination is, for example, 800° C. to 1,200° C.,preferably 900° C. to 1,150° C., and more preferably 950° C. to 1,100°C.

The holding time (hereinafter, also referred to as “calcination time”)at a calcination temperature is preferably 0.5 hours to 5 hours and morepreferably 0.5 hours to 3 hours.

The atmosphere (hereinafter, also referred to as a “calcinationatmosphere”) in the calcination step is preferably an atmosphere otherthan a reducing atmosphere, more preferably at least any of an oxygenatmosphere or an air atmosphere, and still more preferably an airatmosphere.

In the production method of the present embodiment, any of the greenbody or the calcined body (hereinafter, these are also collectivelyreferred to as a green body or the like”) is processed at a temperatureof higher than 1,200° C. to 1,600° C. Accordingly, the green body or thelike becomes a sintered body. Prior to sintering, the green body or thelike may be processed into an arbitrary shape.

Well-known methods can be used for the sintering method and thesintering conditions. Examples of the sintering method include at leastone selected from the group consisting of normal pressure sintering(purssureless sintering), HIP processing, SPS, and vacuum sintering. Thesintering method is preferably normal pressure sintering and morepreferably normal pressure sintering in an air atmosphere since theseare widely used as industrial sintering methods. As the sinteringmethod, it is preferable to perform only normal pressure sintering, andit is more preferable not to perform pressure sintering after normalpressure sintering. Accordingly, it is possible to obtain a sinteredbody as a normal pressure sintered body. The normal pressure sinteringin the present embodiment is a sintering method performed by simplyheating an object to be sintered without applying an external force tothe object during sintering.

The holding temperature (hereinafter, also referred to as a “sinteringtemperature”) during sintering is 1,200° C. to 1,600° C., preferably1,300° C. to 1,580° C., more preferably 1,400° C. to 1,560° C., stillmore preferably 1,430° C. to 1,560° C., and still more preferably 1,480°C. to 1,560° C. In another embodiment, the sintering temperature is1,450° C. to 1,650° C., preferably 1,500° C. to 1,650° C., and morepreferably 1,550° C. to 1,650° C.

The temperature rising rate up to a sintering temperature is, forexample, 50° C./hour to 800° C./hour, preferably 100° C./hour to 800°C./hour, more preferably 150° C./hour to 800° C./hour, still morepreferably 150° C./hour to 700° C./hour.

The holding time (hereinafter, also referred to as a “sintering time”)at a sintering temperature varies depending on the sinteringtemperature, and is preferably 1 hour to 5 hours, more preferably 1 hourto 3 hours, and still more preferably 1 hour to 2 hours.

The atmosphere (hereinafter, also referred to as a “sinteringatmosphere”) of sintering is preferably an atmosphere other than areducing atmosphere, more preferably at least any of an oxygenatmosphere or an air atmosphere, and still more preferably an airatmosphere. The air atmosphere mainly consists of nitrogen and oxygen,and the oxygen concentration is, for example, about 18 to 23 volume %.

Preferred sintering conditions in a sintering step are, for example,normal pressure sintering in an air atmosphere.

EXAMPLES

Hereinafter, the layered body of the present embodiment will bedescribed using examples. However, the present disclosure is not limitedto these examples.

(Warp and Deformation Amount)

A disk-shaped green body, calcined body, or sintered body is used as ameasurement sample to obtain each deformation amount from the followingequation.

Deformation amount=(warp: mm)/dimension: mm)×100

The measurement of a warp was performed through the measurement methodshown in FIG. 3. The measurement sample was disposed so that a convexportion of the measurement sample comes into contact with a horizontalplate. The warp was measured by inserting a thickness gauge (productname: 75A19 manufactured by Nagai Gauge Co., Ltd.) according to JIS B7524:2008 into a gap formed between the horizontal plate and a bottomsurface. The measurement was performed by inserting the gauge disposedparallel to the horizontal plate into the gap formed between thehorizontal plate and the bottom surface of the measurement sample andmeasuring a gauge thickness becoming a maximum thickness of the gaugewhich was able to be inserted into the gap, and the gauge thickness wasregarded as a warp. Warps were measured from gauge thicknesses of 0.03mm, and measured sequentially with an interval of 0.01 mm by using asingle gauge or combining gauges.

For the dimension of the measurement sample, diameters of upper ends anddiameters of lower ends were measured at four points using calipers toobtain an average value of the diameters of the upper and lower ends.

(Total Light Transmittance)

The total light transmittance of a sample was measured through a methodaccording to JIS K 7361. The total light transmittance was measured byirradiating a measurement sample with a standard light source D65 anddetecting a light flux transmitted through the measurement sample usingan integrating sphere. A general haze meter (device name: haze meterNDH2000 manufactured by NIPPON DENSHOKU INDUSTRIES Co., LTD.) was usedfor the measurement.

A disk-shaped sample was used as the measurement sample. Prior to themeasurement, both surfaces of the sample were mirror-polished to obtaina sample thickness of 1 mm and a surface roughness (Ra) of 0.02 μm orless.

(Average Aggregation Size)

The average aggregation size was measured by charging a powder granulesample into a microtrac particle size distribution meter (device name:MT3100II manufactured by MicrotracBEL Corp.) A particle size at whichthe cumulative volume became 50% was regarded as an average aggregationsize.

(Crystal Phase)

The crystal phase of a layered body sample was measured through XRDmeasurement under the following conditions. A general XRD device (devicename: X'pert PRO MPD manufactured by Spectris Co., Ltd.) was used as ameasurement device.

Source: CuK α-rays (λ=1.541862 Å)

Measurement mode: step and scan

Scan condition: 0.000278° per second

Measurement range: 2θ=10-140°

Irradiation width: constant (10 mm)

Rietveld analysis of an obtained XRD pattern was performed usinganalysis software (RIETAN-2000), and the ratio (proportion of anintegrated intensity of a peak) of a tetragonal crystal to a cubiccrystal was obtained. The crystal phase with a highest proportion wasregarded as a main phase.

(ΔL* and ΔC*)

The color tone was measured using a general spectrocolorimeter (devicename: CM-700d manufactured by Konica Minolta, Inc.) The measurementconditions are as follows.

Light source: light source D65

View angle: 10°

Measurement method: SCI.

A disk-shaped sample having a diameter of 20 mm and a thickness of 5.6mm was used as a sintered body sample in the examples, and a disk-shapedsample having a diameter of 20 mm and a thickness of 2.8 mm was used asa sintered body sample in reference examples. Both surfaces of asintered body sample were mirror-polished. A measurement sample wasdisposed on a black plate, both surfaces of the measurement sample afterpolishing were used as evaluation surfaces, and color tones (L*, a*, andb*) of each surface were measured (black background measurement). Anabsolute value of the difference in the measured L* of each surface wasobtained as ΔL*, and an absolute value of the difference in C* obtainedfrom a* and b* was obtained as ΔC*. A diameter of 10 mm was employed asan effective area for evaluating color tones.

Synthesis Example 1 (Synthesis of Zirconia Powder) (Zirconia Powder A1)

A hydrated zirconia sol was obtained by subjecting a zirconiumoxychloride aqueous solution to a hydrolysis reaction. Yttrium chloridewas added to the hydrated zirconia sol so that the yttria concentrationbecame 5.2 mol %, and then, the mixture was dried at 180° C. The driedhydrated zirconia sol was sintered at 1,160° C. for 2 hours, and wasthen washed with distilled water and dried at 110° C. in atmosphericair. α-Alumina, terbium oxide, and distilled water were mixed with theresultant to obtain slurry containing powder containing 0.05 wt % ofalumina, 0.07 wt % of terbium oxide, and the balance being 5.2 mol %yttria-containing zirconia, by processing the mixture with a ball millfor 22 hours.

After the ball mill processing, an acrylic acid-based binder (acrylicresin) was added to and mixed with the slurry as a binding agent so thatthe weight ratio of the binder (binding agent) to the powder mixture inthe slurry became 3.07 wt %. The mixed slurry was spray-dried at 180°C., and powder granules which had an average aggregation size of 45 μmand contained 3.07 wt % of an acrylic acid-based binder (acrylic resin),0.05 wt % of alumina, 0.07 wt % of terbium oxide (0.01 mol % as astabilizer), and the balance being 5.2 mol % yttria-containing zirconiawere obtained.

(Zirconia Powder A2)

Powder granules which had an average aggregation size of 45 μm andcontained 3.04 wt % of an acrylic acid-based binder, 0.05 wt % ofalumina, 0.175 wt % of terbium oxide (0.03 mol % as a stabilizer), andthe balance being 4.75 mol % yttria-containing zirconia were obtainedthrough the same method as that for the zirconia powder A1 except thatthe content of yttria was set to 4.75 mol %, the content of terbiumoxide was set to 0.175 wt %, and the acrylic acid-based binder was addedto and mixed with slurry so that the weight ratio of the binder to theslurry became 3.04 wt %.

(Zirconia Powders A3 to A14)

A hydrated zirconia sol was obtained by subjecting a zirconiumoxychloride aqueous solution to a hydrolysis reaction. Yttrium chlorideand/or erbium oxide were added to the hydrated zirconia sol, and themixture was then dried at 180° C. The dried hydrated zirconia sol wassintered at 1,160° C. for 2 hours, and was then washed with distilledwater and dried at 110° C. in atmospheric air. Terbium oxide and/orcobalt oxide, α-alumina, and distilled water were mixed with theresultant to obtain slurry.

Zirconia powders A3 to A14 which had compositions of the following tableand contained acrylic acid-based binder, alumina, cobalt oxide, terbiumoxide, and the balance being yttria and/or erbia-containing zirconiawere obtained through the same method as that for the zirconia powder A1except that the obtained slurry was used.

TABLE 1 Co₃O₄ Tb₄O₇ (wt % Er₂O₃ (wt % Y₂O₃ Al₂O₃ Binding agent Averageaggregation (wt %) [mol %]) [mol %]) (mol %) (wt %) (wt %) size (μm) A30.001 0.015 [0.003] 0.15 [0.05] 5.35 0.05 3.05 44 A4 0.003 0.040 [0.007]0.35 [0.12] 5.12 0.05 3.04 46 A5 0.007 0.070 [0.012] 0.65 [0.22] 4.820.05 3.03 45 A6 0.002 0.015 [0.003] 0.05 [0.02] 5.41 0.05 3.01 45 A70.003 0.060 [0.010] 0.35 [0.12] 5.04 0.05 3.01 44 A8 0.005 0.025 [0.004]0.05 [0.02] 5.36 0.05 3.02 47 A9 0.015 0.100 [0.017] 0.55 [0.19] 4.750.05 3.05 46 A10 0.005 0.050 [0.008] 0.35 [0.12] 5.08 0.05 3.04 45 A110.007 0.060 [0.010] 0.15 [0.05] 5.15 0.05 3.02 46 A12 0.002 0.015[0.003] 0.05 [0.02] 5.41 0.00 3.02 47 A13 0.003 0.060 [0.010] 0.35[0.12] 5.04 0.01 3.01 44 A14 0.007 0.060 [0.010] 0.15 [0.05] 5.15 0.083.04 44

Synthesis Example 2 (Zirconia Powder B1)

Powder granules which had an average aggregation size of 46 μm andcontained 3.10 wt % of an acrylic acid-based binder, 0.05 wt % ofalumina, 0.07 wt % of terbium oxide (0.01 mol % as a stabilizer), andthe balance being 4.0 mol % yttria-containing zirconia were obtainedthrough the same method as that for the zirconia powder A1 except thatthe content of yttria was set to 4.0 mol % and the acrylic acid-basedbinder was added to and mixed with slurry so that the weight ratio ofthe binder to the slurry became 3.10 wt %.

(Zirconia Powder B2)

Powder granules which had an average aggregation size of 46 μm andcontained 3.07 wt % of an acrylic acid-based binder, 0.05 wt % ofalumina, 0.175 wt % of terbium oxide (0.03 mol % as a stabilizer), andthe balance being 4.0 mol % yttria-containing zirconia were obtainedthrough the same method as that for the zirconia powder A1 except thatthe content of yttria was set to 4.0 mol %, the content of terbium oxidewas set to 0.175 wt %, and the acrylic acid-based binder was added toand mixed with slurry so that the weight ratio of the binder to theslurry became 3.07 wt %.

(Zirconia Powders B3 to B11)

A hydrated zirconia sol was obtained by subjecting a zirconiumoxychloride aqueous solution to a hydrolysis reaction. Yttrium chlorideand erbium oxide were added to the hydrated zirconia sol, and themixture was then dried at 180° C. The dried hydrated zirconia sol wassintered at 1,160° C. for 2 hours, and was then washed with distilledwater and dried at 110° C. in atmospheric air. Terbium oxide and cobaltoxide, α-alumina, and distilled water were mixed with the resultant toobtain slurry.

Zirconia powders B3 to B14 which had compositions of the following tableand contained acrylic acid-based binder, alumina, cobalt oxide, terbiumoxide, and the balance being yttria and erbia-containing zirconia wereobtained through the same method as that for the zirconia powder B1except that the obtained slurry was used.

TABLE 2 Co₃O₄ Tb₄O₇ (wt % Er₂O₃ (wt % Y₂O₃ Al₂O₃ Binding agent Averageaggregation (wt %) [mol %]) [mol %]) (mol %) (wt %) (wt %) size (μm) B30.001 0.015 [0.003] 0.15 [0.05] 3.91 0.05 3.10 48 B4 0.003 0.040 [0.007]0.35 [0.12] 3.77 0.05 3.11 45 B5 0.007 0.070 [0.012] 0.65 [0.22] 3.550.05 3.08 47 B6 0.002 0.015 [0.003] 0.05 [0.02] 3.94 0.05 3.07 47 B70.003 0.060 [0.010] 0.35 [0.12] 3.77 0.05 3.07 46 B8 0.005 0.025 [0.004]0.05 [0.02] 3.85 0.05 3.08 45 B9 0.015 0.100 [0.017] 0.55 [0.19] 3.390.05 3.11 46 B10 0.005 0.050 [0.008] 0.35 [0.12] 3.72 0.05 3.13 44 B110.007 0.060 [0.010] 0.15 [0.05] 3.76 0.05 3.09 48

Synthesis Example 3

A hydrated zirconia sol was obtained by subjecting a zirconiumoxychloride aqueous solution to a hydrolysis reaction. Yttrium chlorideand erbium oxide were added to the hydrated zirconia sol, and themixture was then dried at 180° C. The dried hydrated zirconia sol wassintered at 1,160° C. for 2 hours, and was then washed with distilledwater and dried at 110° C. in atmospheric air. Iron oxyhydroxide and/orcobalt oxide, α-alumina, and distilled water were mixed with theresultant to obtain slurry.

Zirconia powders C1 and C2 which had compositions of the following tableand contained acrylic acid-based binder, alumina, iron oxyhydroxideand/or cobalt oxide, and the balance being yttria and erbia-containingzirconia were obtained through the same method as that for the zirconiapowder A1 except that the obtained slurry was used.

TABLE 3 Fe₂O₃ Co₃O₄ Er₂O₃ (wt % Y₂O₃ Al₂O₃ Binding agent Averageaggregation (wt %) (wt %) [mol %]) (mol %) (wt %) (wt %) size (μm) C10.047 0.003 0.10 [0.03] 5.16 0.05 3.01 46 C2 0.062 0 0.17 [0.06] 5.030.05 3.02 48

Synthesis Example 4

Zirconia powders D1 and D2 which contained acrylic acid-based binder,alumina, iron oxyhydroxide and/or cobalt oxide, and the balance beingyttria and erbia-containing zirconia were obtained through the samemethod as that in Synthesis Example 3 except that the compositions of acolorant, a stabilizer, and a binding agent were as shown in thefollowing table.

TABLE 4 Fe₂O₃ Co₃O₄ Er₂O₃ (wt % Y₂O₃ Al₂O₃ Binding agent Averageaggregation (wt %) (wt %) [mol %]) (mol %) (wt %) (wt %) size (μm) D10.047 0.003 0.10 [0.03] 3.89 0.05 3.06 45 D2 0.062 0 0.17 [0.06] 3.930.05 3.07 44

Example 1 (Green Body)

A mold having an inner diameter of 48 mm was filled with 25 g ofzirconia powder A1, and was then tapped to form a first powder layer.The mold was filled with the same amount of zirconia powder B1 on thefirst powder layer and tapped. Then, uniaxial press molding wasperformed at a pressure of 98 MPa. Thereafter, CIP processing wasperformed at a pressure of 196 MPa to obtain a layered body consistingof two layers, and the obtained layered body was regarded as a greenbody of the present example. The stabilizer content of the first powderlayer was 5.21 mol % and the stabilizer content of the second powderlayer was 4.01 mol %. The difference in the yttria content between thelayers was 1.2 mol %, and the difference in the binder content was 0.02wt %. In addition, the colorant content of all of the green body of thepresent example, the first powder layer, and the second powder layer was0.07 wt %.

(Calcined Body)

The green body was calcined at a temperature rising rate of 20° C./hour,a calcination temperature of 1,000° C., and a calcination time of 2hours in atmospheric air to obtain a layered body which was regarded asa calcined body of the present example.

(Sintered Body)

The calcined body was sintered at a temperature rising rate of 100°C./hour, a sintering temperature of 1,500° C., and a sintering time of 2hours in atmospheric air to obtain a layered body which was regarded asa sintered body of the present example.

The stabilizer content of the sintered body was 4.6 mol %. It wasconfirmed that ΔL* and ΔC* of the sintered body of the present examplewere respectively 2.33 and 2.64 and that the sintered body was a layeredbody having a change in color tone.

The warp was less than a measurement limit (less than 0.03 mm) for allof the green body, the calcined body, and the sintered body.

Example 2

A mold having an inner diameter of 48 mm was filled with 25 g ofzirconia powder A2, and was then tapped to form a first powder layer.The mold was filled with the same amount of zirconia powder B2 on thefirst powder layer and tapped. Then, uniaxial press molding wasperformed at a pressure of 49 MPa. Thereafter, CIP processing wasperformed at a pressure of 196 MPa to obtain a layered body which wasregarded as a green body of the present example. The stabilizer contentof the first powder layer was 4.78 mol % and the stabilizer content ofthe second powder layer was 4.03 mol %. The difference in the yttriacontent between the layers was 0.75 mol %, and the difference in thebinder content was 0.03 wt %. In addition, the color pigment content ofall of the green body of the present example, the first powder layer,and the second powder layer was 0.175 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used.

The stabilizer content of the sintered body was 4.375 mol %. It wasconfirmed that ΔL* and ΔC* of the sintered body of the present examplewere respectively 1.13 and 0.34 and that the sintered body was a layeredbody having a change in color tone.

In can be seen from these examples that a layered body to which a changein color tone is imparted is obtained even though the contents ofcolorants in the layers are equal to each other.

Example 3

A green body of the present embodiment of which the stabilizer contentof a first powder layer was 5.40 mol %, the stabilizer content of asecond powder layer was 3.96 mol %, the difference in the stabilizercontent between the layers was 1.44 mol %, and the difference in theamount of a binding agent was 0.05 wt % was obtained through the samemethod as in Example 1 except that the zirconia powders A3 and B3 wereused instead of the zirconia powders A1 and B1. The colorant content ofall of the green body of the present example, the first powder layer,and the second powder layer was 0.166 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used. Thestabilizer content of the sintered body was 4.68 mol %.

ΔL* and ΔC* of the sintered body are respectively 3.99 and 2.16, and thesintered body is a layered body having a change in color tone. Inaddition, the warp was less than a measurement limit (less than 0.03 mm)for all of the green body, the calcined body, and the sintered body.

Example 4

A green body of the present embodiment of which the stabilizer contentof a first powder layer was 5.25 mol %, the stabilizer content of asecond powder layer was 3.90 mol %, the difference in the stabilizercontent between the layers was 1.35 mol %, and the difference in theamount of a binding agent was 0.07 wt % was obtained through the samemethod as in Example 1 except that the zirconia powders A4 and B4 wereused instead of the zirconia powders A1 and B1. The colorant content ofall of the green body of the present example, the first powder layer,and the second powder layer was 0.393 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used. Thestabilizer content of the sintered body was 4.58 mol %.

ΔL* and ΔC* of the sintered body are respectively 3.32 and 1.91, and thesintered body is a layered body having a change in color tone. Inaddition, the warp was less than a measurement limit (less than 0.03 mm)for all of the green body, the calcined body, and the sintered body.

Example 5

A green body of the present embodiment of which the stabilizer contentof a first powder layer was 5.05 mol %, the stabilizer content of asecond powder layer was 3.78 mol %, the difference in the stabilizercontent between the layers was 1.27 mol %, and the difference in theamount of a binding agent was 0.05 wt % was obtained through the samemethod as in Example 1 except that the zirconia powders A5 and B5 wereused instead of the zirconia powders A1 and B1. The colorant content ofall of the green body of the present example, the first powder layer,and the second powder layer was 0.727 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used. Thestabilizer content of the sintered body was 4.42 mol %.

ΔL* and ΔC* of the sintered body are respectively 2.96 and 1.86, and thesintered body is a layered body having a change in color tone. Inaddition, the warp was less than a measurement limit (less than 0.03 mm)for all of the green body, the calcined body, and the sintered body.

Example 6

A green body of the present embodiment of which the stabilizer contentof a first powder layer was 5.43 mol %, the stabilizer content of asecond powder layer was 3.96 mol %, the difference in the stabilizercontent between the layers was 1.47 mol %, and the difference in theamount of a binding agent was 0.06 wt % was obtained through the samemethod as in Example 1 except that the zirconia powders A6 and B6 wereused instead of the zirconia powders A1 and B1. The colorant content ofall of the green body of the present example, the first powder layer,and the second powder layer was 0.067 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used. Thestabilizer content of the sintered body was 4.69 mol %.

ΔL* and ΔC* of the sintered body are respectively 4.20 and 2.80, and thesintered body is a layered body having a change in color tone. Inaddition, the warp was less than a measurement limit (less than 0.03 mm)for all of the green body, the calcined body, and the sintered body.

Example 7

A green body of the present embodiment of which the stabilizer contentof a first powder layer was 5.17 mol %, the stabilizer content of asecond powder layer was 3.91 mol %, the difference in the stabilizercontent between the layers was 1.26 mol %, and the difference in theamount of a binding agent was 0.06 wt % was obtained through the samemethod as in Example 1 except that the zirconia powders A7 and B7 wereused instead of the zirconia powders A1 and B1. The colorant content ofall of the green body of the present example, the first powder layer,and the second powder layer was 0.413 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used. Thestabilizer content of the sintered body was 4.54 mol %.

ΔL* and ΔC* of the sintered body are respectively 3.10 and 2.09, and thesintered body is a layered body having a change in color tone. Inaddition, the warp was less than a measurement limit (less than 0.03 mm)for all of the green body, the calcined body, and the sintered body.

Example 8

A green body of the present embodiment of which the stabilizer contentof a first powder layer was 5.38 mol %, the stabilizer content of asecond powder layer was 3.87 mol %, the difference in the stabilizercontent between the layers was 1.51 mol %, and the difference in theamount of a binding agent was 0.06 wt % was obtained through the samemethod as in Example 1 except that the zirconia powders A8 and B8 wereused instead of the zirconia powders A1 and B1. The colorant content ofall of the green body of the present example, the first powder layer,and the second powder layer was 0.08 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used. Thestabilizer content of the sintered body was 4.63 mol %.

ΔL* and ΔC* of the sintered body are respectively 3.67 and 2.37, and thesintered body is a layered body having a change in color tone. Inaddition, the warp was less than a measurement limit (less than 0.03 mm)for all of the green body, the calcined body, and the sintered body.

Example 9

A green body of the present embodiment of which the stabilizer contentof a first powder layer was 4.95 mol %, the stabilizer content of asecond powder layer was 3.59 mol %, the difference in the stabilizercontent between the layers was 1.36 mol %, and the difference in theamount of a binding agent was 0.06 wt % was obtained through the samemethod as in Example 1 except that the zirconia powders A9 and B9 wereused instead of the zirconia powders A1 and B1. The colorant content ofall of the green body of the present example, the first powder layer,and the second powder layer was 0.665 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used. Thestabilizer content of the sintered body was 4.27 mol %.

ΔL* and ΔC* of the sintered body are respectively 2.20 and 2.64, and thesintered body is a layered body having a change in color tone. Inaddition, the warp was less than a measurement limit (less than 0.03 mm)for all of the green body, the calcined body, and the sintered body.

Example 10

A green body of the present embodiment of which the stabilizer contentof a first powder layer was 5.21 mol %, the stabilizer content of asecond powder layer was 3.85 mol %, the difference in the stabilizercontent between the layers was 1.36 mol %, and the difference in theamount of a binding agent was 0.09 wt % was obtained through the samemethod as in Example 1 except that the zirconia powders A10 and B10 wereused instead of the zirconia powders A1 and B1. The colorant content ofall of the green body of the present example, the first powder layer,and the second powder layer was 0.405 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used. Thestabilizer content of the sintered body was 4.53 mol %.

ΔL* and ΔC* of the sintered body are respectively 3.70 and 1.83, and thesintered body is a layered body having a change in color tone. Inaddition, the warp was less than a measurement limit (less than 0.03 mm)for all of the green body, the calcined body, and the sintered body.

Example 11

A green body of the present embodiment of which the stabilizer contentof a first powder layer was 5.22 mol %, the stabilizer content of asecond powder layer was 3.82 mol %, the difference in the stabilizercontent between the layers was 1.39 mol %, and the difference in theamount of a binding agent was 0.07 wt % was obtained through the samemethod as in Example 1 except that the zirconia powders A11 and B11 wereused instead of the zirconia powders A1 and B1. The colorant content ofall of the green body of the present example, the first powder layer,and the second powder layer was 0.217 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used. Thestabilizer content of the sintered body was 4.52 mol %.

ΔL* and ΔC* of the sintered body are respectively 3.30 and 2.28, and thesintered body is a layered body having a change in color tone. Inaddition, the warp was less than a measurement limit (less than 0.03 mm)for all of the green body, the calcined body, and the sintered body.

Example 12

A green body of the present embodiment of which the stabilizer contentof a first powder layer was 5.40 mol %, the stabilizer content of asecond powder layer was 3.96 mol %, the difference in the stabilizercontent between the layers was 1.44 mol %, and the difference in theamount of a binding agent was 0.05 wt % was obtained through the samemethod as in Example 1 except that a mold having an inner diameter of110 mm was used, uniaxial press molding was performed at a pressure of19.8 MPa, and the zirconia powders A3 and B3 were used instead of thezirconia powders A1 and B1. The colorant content of all of the greenbody of the present example, the first powder layer, and the secondpowder layer was 0.166 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used. Thestabilizer content of the sintered body was 4.68 mol %.

ΔL* and ΔC* of the sintered body are respectively 3.99 and 2.16, and thesintered body is a layered body having a change in color tone. The warpsof the green body, the calcined body, and the sintered body wererespectively 0.05 mm, 0.09 mm, and 0.05 mm, and the deformation amountsthereof were respectively 0.05, 0.09, and 0.06.

Example 13

A green body of the present embodiment of which the stabilizer contentof a first powder layer was 5.43 mol %, the stabilizer content of asecond powder layer was 3.96 mol %, the difference in the stabilizercontent between the layers was 1.47 mol %, and the difference in theamount of a binding agent was 0.06 wt % was obtained through the samemethod as in Example 1 except that a mold having an inner diameter of110 mm was used and the zirconia powders A6 and B6 were used. Thecolorant content of all of the green body of the present example, thefirst powder layer, and the second powder layer was 0.067 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used. Thestabilizer content of the sintered body was 4.69 mol %.

ΔL* and ΔC* of the sintered body are respectively 4.20 and 2.80, and thesintered body is a layered body having a change in color tone. Inaddition, the warp was less than a measurement limit (less than 0.03 mm)for all of the green body and the sintered body. However, the calcinedbody had a warp of 0.06 mm and a deformation amount of 0.06.

Example 14

A green body of the present embodiment of which the stabilizer contentof a first powder layer was 5.17 mol %, the stabilizer content of asecond powder layer was 3.91 mol %, the difference in the stabilizercontent between the layers was 1.26 mol %, and the difference in theamount of a binding agent was 0.06 wt % was obtained through the samemethod as in Example 1 except that a mold having an inner diameter of110 mm was used and the zirconia powders A13 and B7 were used. Thecolorant content of all of the green body of the present example, thefirst powder layer, and the second powder layer was 0.413 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used. Thestabilizer content of the sintered body was 4.54 mol %.

ΔL* and ΔC* of the sintered body are respectively 3.27 and 2.25, and thesintered body is a layered body having a change in color tone. Inaddition, the warp was less than a measurement limit (less than 0.03 mm)for all of the green body and the sintered body. However, the calcinedbody had a warp of 0.19 mm and a deformation amount of 0.18.

Example 15

A green body of the present embodiment of which the stabilizer contentof a first powder layer was 5.22 mol %, the stabilizer content of asecond powder layer was 3.82 mol %, the difference in the stabilizercontent between the layers was 1.40 mol %, and the difference in theamount of a binding agent was 0.05 wt % was obtained through the samemethod as in Example 1 except that a mold having an inner diameter of110 mm was used and the zirconia powders A14 and B11 were used. Thecolorant content of all of the green body of the present example, thefirst powder layer, and the second powder layer was 0.217 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used. Thestabilizer content of the sintered body was 4.52 mol %.

ΔL* and ΔC* of the sintered body are respectively 3.14 and 2.22, and thesintered body is a layered body having a change in color tone. Inaddition, the green body had a warp of less than a measurement limit(less than 0.03 mm). However, the calcined body and the sintered bodyrespectively had warps of 0.19 mm and 0.03 mm and respectively haddeformation amounts of 0.18 and 0.04.

It was confirmed from these examples that the warp of a calcined bodytends to be particularly suppressed as the difference in the content ofalumina between layers is smaller.

Example 16

A green body of the present embodiment of which the stabilizer contentof a first powder layer was 5.19 mol %, the stabilizer content of asecond powder layer was 3.93 mol %, the difference in the stabilizercontent between the layers was 1.26 mol %, and the difference in theamount of a binding agent was 0.05 wt % was obtained through the samemethod as in Example 1 except that a mold having an inner diameter of110 mm was used, uniaxial press molding was performed at a pressure of98 MPa, and the zirconia powders C1 and D1 were used instead of thezirconia powders A1 and B1. The colorant content of all of the greenbody of the present example, the first powder layer, and the secondpowder layer was 0.150 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used. Thestabilizer content of the sintered body was 4.56 mol %.

ΔL* and ΔC* of the sintered body are respectively 4.27 and 2.92, and thesintered body is a layered body having a change in color tone. Inaddition, the warp was less than a measurement limit (less than 0.03 mm)for all of the green body and the sintered body. However, the calcinedbody had a warp of 0.12 mm and a deformation amount of 0.11.

Example 17

A green body of the present embodiment of which the stabilizer contentof a first powder layer was 5.09 mol %, the stabilizer content of asecond powder layer was 3.99 mol %, the difference in the stabilizercontent between the layers was 1.10 mol %, and the difference in theamount of a binding agent was 0.05 wt % was obtained through the samemethod as in Example 1 except that a mold having an inner diameter of110 mm was used, uniaxial press molding was performed at a pressure of98 MPa, and the zirconia powders C2 and D2 were used instead of thezirconia powders A1 and B1. The colorant content of all of the greenbody of the present example, the first powder layer, and the secondpowder layer was 0.232 wt %.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used. Thestabilizer content of the sintered body was 4.54 mol %.

ΔL* and ΔC* of the sintered body are respectively 4.93 and 2.71, and thesintered body is a layered body having a change in color tone. Inaddition, the warp was less than a measurement limit (less than 0.03 mm)for all of the green body and the sintered body. However, the calcinedbody had a warp of 0.16 mm and a deformation amount of 0.15.

Comparative Example 1

A mold having an inner diameter of 110 mm was filled with 25 g ofzirconia powder consisting of 0.094 wt % of iron oxide, 0.0045 wt % ofcobalt oxide, and the balance being 4 mol % yttria-containing zirconia,and was then tapped to form a first powder layer. The mold was filledwith the same amount of zirconia powder consisting of 4 mol %yttria-containing zirconia on the first powder layer and tapped to forma second powder layer. Then, uniaxial press molding was performed at apressure of 98 MPa. Thereafter, CIP processing was performed at apressure of 196 MPa to obtain a layered body consisting of two layers,and the obtained layered body was regarded as a green body of thepresent comparative example. The difference in the yttria contentbetween the layers was 0 mol % and the difference in the amount of thebinding agent between the layers was 0.02 wt %.

A calcined body was produced through the same method as in Example 1except that the green body was used. The warp of the calcined body was0.67 mm.

There was a large warp generated in the calcined body of the presentcomparative example in which the first layer and the second layer havethe same yttria content as each other and have different colorantcontents by 0.139 wt %.

Reference Example 1

The mold having an inner diameter of 48 mm was filled with the zirconiapowder A1 and tapped. Then, uniaxial press molding was performed at apressure of 49 MPa. Thereafter, CIP processing was performed at apressure of 196 MPa to obtain a green body.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used.

The obtained sintered body contained 0.05 wt % of alumina and thebalance being 5.2 mol % yttria and 0.01 mol % terbium oxide-containingzirconia. The crystal phase of the sintered body consisted of atetragonal crystal and a cubic crystal while the tetragonal crystal wasa main phase. In addition, the total light transmittance of the sinteredbody was 42%.

Reference Example 2

The mold having an inner diameter of 48 mm was filled with the zirconiapowder A2 and tapped. Then, uniaxial press molding was performed at apressure of 49 MPa. Thereafter, CIP processing was performed at apressure of 196 MPa to obtain a green body.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used.

The obtained sintered body contained 0.05 wt % of alumina and thebalance being 4.75 mol % yttria and 0.03 mol % terbium oxide-containingzirconia. The crystal phase of the sintered body consisted of atetragonal crystal and a cubic crystal while the tetragonal prime was amain phase. In addition, the total light transmittance of the sinteredbody was 40%.

Reference Example 3

The mold having an inner diameter of 48 mm was filled with the zirconiapowder B1 and tapped. Then, uniaxial press molding was performed at apressure of 49 MPa. Thereafter, CIP processing was performed at apressure of 196 MPa to obtain a green body.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used.

The obtained sintered body contained 0.05 wt % of alumina and thebalance being 4.0 mol % yttria and 0.01 mol % terbium oxide-containingzirconia. The crystal phase of the sintered body consisted of atetragonal crystal and a cubic crystal while the tetragonal crystal wasa main phase. In addition, the color tones of the sintered body were78.51 for L*, 0.18 for a*, and 25.06 for b*, and the total lighttransmittance was 40%.

Reference Example 4

The mold having an inner diameter of 48 mm was filled with the zirconiapowder B2 and tapped. Then, uniaxial press molding was performed at apressure of 49 MPa. Thereafter, CIP processing was performed at apressure of 196 MPa to obtain a greenbody.

A calcined body and a sintered body were obtained through the samemethod as in Example 1 except that the green body was used.

The obtained sintered body contained 0.05 wt % of alumina and thebalance being 4.0 mol % yttria and 0.03 mol % terbium oxide-containingzirconia. The crystal phase of the sintered body consisted of atetragonal crystal and a cubic crystal while the cubic crystal was amain phase. In addition, the color tones of the sintered body were 77.88for L*, 6.02 for a*, and 31.70 for b*, and the total light transmittancewas 38%.

The entire contents of the specifications, claims, drawings, andabstracts of Japanese Patent Application Nos. 2019-041310 and2019-041321, filed Mar. 7, 2019 are incorporated by reference as adisclosure of the specification of the present disclosure.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as being limited bythe foregoing description, and is only limited by the scope of theappended claims.

EXPLANATION OF REFERENCES

-   -   100, 200, 300, 400: zirconia sintered body    -   11, 21: first layer    -   12, 22: second layer    -   23: third layer    -   32A, 32B: thickness gauge    -   33: size of sintered body    -   41: load    -   42: fulcrum points distance    -   51: zirconia having necking structure.

What is claimed is:
 1. A layered body which has a structure, in whichtwo or more layers containing stabilizer-containing zirconia and acolorant are layered, and in which types and contents of the colorantscontained in the layers are equal to each other, the layered bodycomprising at least: a first layer containing a colorant and zirconiawhich has a stabilizer content of higher than or equal to 3.3 mol %; anda second layer containing a colorant and zirconia which has a stabilizercontent different from that of the zirconia contained in the firstlayer.
 2. The layered body according to claim 1, wherein the content ofthe stabilizer of the stabilizer-containing zirconia contained in thesecond layer is 1.5 mol % to 7.0 mol %.
 3. The layered body according toclaim 1, wherein the content of the stabilizer of thestabilizer-containing zirconia contained in the second layer is 4.5 mol% to 7.0 mol %.
 4. The layered body according to claim 1, wherein thecontent of the stabilizer of the stabilizer-containing zirconiacontained in the first layer is 3.3 mol % to 5.5 mol %.
 5. The layeredbody according to claim 1, wherein a difference between the stabilizercontent in the first layer and the stabilizer content in the secondlayer is greater than or equal to 0.2 mol %.
 6. The layered bodyaccording to claim 1, wherein the stabilizer is one or more selectedfrom the group consisting of yttria (Y₂O₃), calcia (CaO), magnesia(MgO), ceria (CeO₂), praseodymium oxide (Pr₆O₁₁), neodymium oxide(Nd₂O₃), terbium oxide (Tb₄O₇), erbium oxide (Er₂O₃), and ytterbiumoxide (Yb₂O₃).
 7. The layered body according to claim 1, wherein thecolorant is at least any of a transition metal element or alanthanoid-based rare earth element.
 8. The layered body according toclaim 1, wherein the content of the colorant is 0.01 wt % to 1.0 wt %.9. The layered body according to claim 1, wherein at least one of thelayers contains alumina.
 10. The layered body according to claim 1,wherein a warp measured using a thickness gauge according to JIS B7524:2008 is less than or equal to 1.0 mm.
 11. The layered bodyaccording to claim 1, wherein a warp measured using a thickness gaugeaccording to JIS B 7524:2008 is less than or equal to 0.2 mm.
 12. Thelayered body according to claim 1, wherein the layered body is asintered body.
 13. The layered body according to claim 1, furthercomprising: a zirconia layer of which a total light transmittance withrespect to a CIE standard light source D65 at a sample thickness of 1.0mm is 30% to 50%.
 14. The layered body according to claim 1, wherein thelayered body is a calcined body.
 15. A method for producing the layeredbody according to claim 1, comprising: a step of sintering a green bodyat 1,200° C. to 1,600° C., wherein the green body has a structure, inwhich two or more powder composition layers consisting of a powdercomposition containing a stabilizer-containing zirconia, a colorant, anda binding agent are layered, and in which types and contents of thecolorants contained in the powder composition layers are equal to eachother, includes at least a first powder composition layer containing abinding agent, a color pigment, and zirconia which has a stabilizercontent of higher than or equal to 3.3 mol % and a second powdercomposition layer containing a binding agent, a colorant, and zirconiawhich has a stabilizer content different from that of the zirconiacontained in the first powder composition layer, and has a difference ina binding agent content between the first powder composition layer andthe second powder composition layer exceeds 0.01 wt %.
 16. A method forproducing the layered body according to claim 1, comprising: a step ofcalcining a green body at a temperature of higher than or equal to 800°C. and lower than 1,200° C. to obtain a calcined body; and a step ofsintering the calcined body at 1,200° C. to 1,600° C., wherein the greenbody has a structure, in which two or more powder composition layersconsisting of a powder composition containing a stabilizer-containingzirconia, a colorant, and a binding agent are layered, and in whichtypes and contents of the colorants contained in the powder compositionlayers are equal to each other, includes at least a first powdercomposition layer containing a binding agent, a colorant, and zirconiawhich has a stabilizer content of higher than or equal to 3.3 mol % anda second powder composition layer containing a binding agent, acolorant, and zirconia which has a stabilizer content different fromthat of the zirconia contained in the first powder composition layer,and has a difference in a binding agent content between the first powdercomposition layer and the second powder composition layer exceeds 0.01wt %.
 17. A method for producing the layered body according to claim 1,comprising: a step of calcining a green body at a temperature of higherthan or equal to 800° C. and lower than 1,200° C., wherein the greenbody has a structure, in which two or more powder composition layersconsisting of a powder composition containing a stabilizer-containingzirconia, a colorant, and a binding agent are layered, and in whichtypes and contents of the colorants contained in the powder compositionlayers are equal to each other, includes at least a first powdercomposition layer containing a binding agent, a colorant, and zirconiawhich has a stabilizer content of higher than or equal to 3.3 mol % anda second powder composition layer containing a binding agent, acolorant, and zirconia which has a stabilizer content different fromthat of the zirconia contained in the first powder composition layer,and has a difference in a binding agent content between the first powdercomposition layer and the second powder composition layer exceeds 0.01wt %.
 18. The production method according to claim 15, wherein thebinding agent is one or more selected from the group consisting ofpolyvinyl alcohol, polyvinyl butyrate, wax, and acrylic resin.
 19. Theproduction method according to claim 15, wherein the powder compositioncontained in the powder composition layers is granulated powder.
 20. Adental material containing the layered body according to claim 1.